Description of the different parameters to the ZFS module.
dbuf_cache_max_bytes (ulong)
Maximum size in bytes of the dbuf cache. The target size
is determined by the MIN versus
1/2^dbuf_cache_shift (1/32) of the
target ARC size. The behavior of the dbuf cache and its associated settings
can be observed via the
/proc/spl/kstat/zfs/dbufstats kstat.
Default value: ULONG_MAX.
dbuf_metadata_cache_max_bytes (ulong)
Maximum size in bytes of the metadata dbuf cache. The
target size is determined by the MIN versus
1/2^dbuf_metadata_cache_shift (1/64) of the target ARC size. The
behavior of the metadata dbuf cache and its associated settings can be
observed via the
/proc/spl/kstat/zfs/dbufstats kstat.
Default value: ULONG_MAX.
dbuf_cache_hiwater_pct (uint)
The percentage over
dbuf_cache_max_bytes when
dbufs must be evicted directly.
Default value: 10%.
dbuf_cache_lowater_pct (uint)
The percentage below
dbuf_cache_max_bytes when the
evict thread stops evicting dbufs.
Default value: 10%.
dbuf_cache_shift (int)
Set the size of the dbuf cache,
dbuf_cache_max_bytes, to a log2 fraction of the target ARC size.
Default value: 5.
dbuf_metadata_cache_shift (int)
Set the size of the dbuf metadata cache,
dbuf_metadata_cache_max_bytes, to a log2 fraction of the target ARC
size.
Default value: 6.
dmu_object_alloc_chunk_shift (int)
dnode slots allocated in a single operation as a power of
2. The default value minimizes lock contention for the bulk operation
performed.
Default value: 7 (128).
dmu_prefetch_max (int)
Limit the amount we can prefetch with one call to this
amount (in bytes). This helps to limit the amount of memory that can be used
by prefetching.
Default value: 134,217,728 (128MB).
ignore_hole_birth (int)
This is an alias for
send_holes_without_birth_time.
l2arc_feed_again (int)
Turbo L2ARC warm-up. When the L2ARC is cold the fill
interval will be set as fast as possible.
Use 1 for yes (default) and 0 to disable.
l2arc_feed_min_ms (ulong)
Min feed interval in milliseconds. Requires
l2arc_feed_again=1 and only applicable in related situations.
Default value: 200.
l2arc_feed_secs (ulong)
Seconds between L2ARC writing
Default value: 1.
l2arc_headroom (ulong)
How far through the ARC lists to search for L2ARC
cacheable content, expressed as a multiplier of
l2arc_write_max. ARC
persistence across reboots can be achieved with persistent L2ARC by setting
this parameter to
0 allowing the full length of ARC lists to be
searched for cacheable content.
Default value: 2.
l2arc_headroom_boost (ulong)
Scales
l2arc_headroom by this percentage when
L2ARC contents are being successfully compressed before writing. A value of
100 disables this feature.
Default value: 200%.
l2arc_mfuonly (int)
Controls whether only MFU metadata and data are cached
from ARC into L2ARC. This may be desired to avoid wasting space on L2ARC when
reading/writing large amounts of data that are not expected to be accessed
more than once. The default is
0, meaning both MRU and MFU data and
metadata are cached. When turning off (
0) this feature some MRU buffers
will still be present in ARC and eventually cached on L2ARC.
Use 0 for no (default) and 1 for yes.
l2arc_meta_percent (int)
Percent of ARC size allowed for L2ARC-only headers. Since
L2ARC buffers are not evicted on memory pressure, too large amount of headers
on system with irrationaly large L2ARC can render it slow or unusable. This
parameter limits L2ARC writes and rebuild to achieve it.
Default value: 33%.
l2arc_trim_ahead (ulong)
Trims ahead of the current write size
(
l2arc_write_max) on L2ARC devices by this percentage of write size if
we have filled the device. If set to
100 we TRIM twice the space
required to accommodate upcoming writes. A minimum of 64MB will be trimmed. It
also enables TRIM of the whole L2ARC device upon creation or addition to an
existing pool or if the header of the device is invalid upon importing a pool
or onlining a cache device. A value of
0 disables TRIM on L2ARC
altogether and is the default as it can put significant stress on the
underlying storage devices. This will vary depending of how well the specific
device handles these commands.
Default value: 0%.
l2arc_noprefetch (int)
Do not write buffers to L2ARC if they were prefetched but
not used by applications.
Use 1 for yes (default) and 0 to disable.
l2arc_norw (int)
No reads during writes.
Use 1 for yes and 0 for no (default).
l2arc_write_boost (ulong)
Cold L2ARC devices will have
l2arc_write_max
increased by this amount while they remain cold.
Default value: 8,388,608.
l2arc_write_max (ulong)
Max write bytes per interval.
Default value: 8,388,608.
l2arc_rebuild_enabled (int)
Rebuild the L2ARC when importing a pool (persistent
L2ARC). This can be disabled if there are problems importing a pool or
attaching an L2ARC device (e.g. the L2ARC device is slow in reading stored log
metadata, or the metadata has become somehow fragmented/unusable).
Use 1 for yes (default) and 0 for no.
l2arc_rebuild_blocks_min_l2size (ulong)
Min size (in bytes) of an L2ARC device required in order
to write log blocks in it. The log blocks are used upon importing the pool to
rebuild the L2ARC (persistent L2ARC). Rationale: for L2ARC devices less than
1GB, the amount of data l2arc_evict() evicts is significant compared to the
amount of restored L2ARC data. In this case do not write log blocks in L2ARC
in order not to waste space.
Default value: 1,073,741,824 (1GB).
metaslab_aliquot (ulong)
Metaslab granularity, in bytes. This is roughly similar
to what would be referred to as the "stripe size" in traditional
RAID arrays. In normal operation, ZFS will try to write this amount of data to
a top-level vdev before moving on to the next one.
Default value: 524,288.
metaslab_bias_enabled (int)
Enable metaslab group biasing based on its vdev's over-
or under-utilization relative to the pool.
Use 1 for yes (default) and 0 for no.
metaslab_force_ganging (ulong)
Make some blocks above a certain size be gang blocks.
This option is used by the test suite to facilitate testing.
Default value: 16,777,217.
zfs_history_output_max (int)
When attempting to log the output nvlist of an ioctl in
the on-disk history, the output will not be stored if it is larger than size
(in bytes). This must be less then DMU_MAX_ACCESS (64MB). This applies
primarily to zfs_ioc_channel_program().
Default value: 1MB.
zfs_keep_log_spacemaps_at_export (int)
Prevent log spacemaps from being destroyed during pool
exports and destroys.
Use 1 for yes and 0 for no (default).
zfs_metaslab_segment_weight_enabled (int)
Enable/disable segment-based metaslab selection.
Use 1 for yes (default) and 0 for no.
zfs_metaslab_switch_threshold (int)
When using segment-based metaslab selection, continue
allocating from the active metaslab until
zfs_metaslab_switch_threshold
worth of buckets have been exhausted.
Default value: 2.
metaslab_debug_load (int)
Load all metaslabs during pool import.
Use 1 for yes and 0 for no (default).
metaslab_debug_unload (int)
Prevent metaslabs from being unloaded.
Use 1 for yes and 0 for no (default).
metaslab_fragmentation_factor_enabled (int)
Enable use of the fragmentation metric in computing
metaslab weights.
Use 1 for yes (default) and 0 for no.
metaslab_df_max_search (int)
Maximum distance to search forward from the last offset.
Without this limit, fragmented pools can see >100,000 iterations and
metaslab_block_picker() becomes the performance limiting factor on
high-performance storage.
With the default setting of 16MB, we typically see less than 500
iterations, even with very fragmented, ashift=9 pools. The maximum number of
iterations possible is: metaslab_df_max_search / (2 *
(1<<ashift)). With the default setting of 16MB this is 16*1024
(with ashift=9) or 2048 (with ashift=12).
Default value: 16,777,216 (16MB)
metaslab_df_use_largest_segment (int)
If we are not searching forward (due to
metaslab_df_max_search, metaslab_df_free_pct, or metaslab_df_alloc_threshold),
this tunable controls what segment is used. If it is set, we will use the
largest free segment. If it is not set, we will use a segment of exactly the
requested size (or larger).
Use 1 for yes and 0 for no (default).
zfs_metaslab_max_size_cache_sec (ulong)
When we unload a metaslab, we cache the size of the
largest free chunk. We use that cached size to determine whether or not to
load a metaslab for a given allocation. As more frees accumulate in that
metaslab while it's unloaded, the cached max size becomes less and less
accurate. After a number of seconds controlled by this tunable, we stop
considering the cached max size and start considering only the histogram
instead.
Default value: 3600 seconds (one hour)
zfs_metaslab_mem_limit (int)
When we are loading a new metaslab, we check the amount
of memory being used to store metaslab range trees. If it is over a threshold,
we attempt to unload the least recently used metaslab to prevent the system
from clogging all of its memory with range trees. This tunable sets the
percentage of total system memory that is the threshold.
Default value: 25 percent
zfs_vdev_default_ms_count (int)
When a vdev is added target this number of metaslabs per
top-level vdev.
Default value: 200.
zfs_vdev_default_ms_shift (int)
Default limit for metaslab size.
Default value: 29 [meaning (1 << 29) = 512MB].
zfs_vdev_max_auto_ashift (ulong)
Maximum ashift used when optimizing for logical ->
physical sector size on new top-level vdevs.
Default value: ASHIFT_MAX (16).
zfs_vdev_min_auto_ashift (ulong)
Minimum ashift used when creating new top-level vdevs.
Default value: ASHIFT_MIN (9).
zfs_vdev_min_ms_count (int)
Minimum number of metaslabs to create in a top-level
vdev.
Default value: 16.
vdev_validate_skip (int)
Skip label validation steps during pool import. Changing
is not recommended unless you know what you are doing and are recovering a
damaged label.
Default value: 0.
zfs_vdev_ms_count_limit (int)
Practical upper limit of total metaslabs per top-level
vdev.
Default value: 131,072.
metaslab_preload_enabled (int)
Enable metaslab group preloading.
Use 1 for yes (default) and 0 for no.
metaslab_lba_weighting_enabled (int)
Give more weight to metaslabs with lower LBAs, assuming
they have greater bandwidth as is typically the case on a modern constant
angular velocity disk drive.
Use 1 for yes (default) and 0 for no.
metaslab_unload_delay (int)
After a metaslab is used, we keep it loaded for this many
txgs, to attempt to reduce unnecessary reloading. Note that both this many
txgs and
metaslab_unload_delay_ms milliseconds must pass before
unloading will occur.
Default value: 32.
metaslab_unload_delay_ms (int)
After a metaslab is used, we keep it loaded for this many
milliseconds, to attempt to reduce unnecessary reloading. Note that both this
many milliseconds and
metaslab_unload_delay txgs must pass before
unloading will occur.
Default value: 600000 (ten minutes).
send_holes_without_birth_time (int)
When set, the hole_birth optimization will not be used,
and all holes will always be sent on zfs send. This is useful if you suspect
your datasets are affected by a bug in hole_birth.
Use 1 for on (default) and 0 for off.
spa_config_path (charp)
SPA config file
Default value: /etc/zfs/zpool.cache.
spa_asize_inflation (int)
Multiplication factor used to estimate actual disk
consumption from the size of data being written. The default value is a worst
case estimate, but lower values may be valid for a given pool depending on its
configuration. Pool administrators who understand the factors involved may
wish to specify a more realistic inflation factor, particularly if they
operate close to quota or capacity limits.
Default value: 24.
spa_load_print_vdev_tree (int)
Whether to print the vdev tree in the debugging message
buffer during pool import. Use 0 to disable and 1 to enable.
Default value: 0.
spa_load_verify_data (int)
Whether to traverse data blocks during an "extreme
rewind" (
-X) import. Use 0 to disable and 1 to enable.
An extreme rewind import normally performs a full traversal of all
blocks in the pool for verification. If this parameter is set to 0, the
traversal skips non-metadata blocks. It can be toggled once the import has
started to stop or start the traversal of non-metadata blocks.
Default value: 1.
spa_load_verify_metadata (int)
Whether to traverse blocks during an "extreme
rewind" (
-X) pool import. Use 0 to disable and 1 to enable.
An extreme rewind import normally performs a full traversal of all
blocks in the pool for verification. If this parameter is set to 0, the
traversal is not performed. It can be toggled once the import has started to
stop or start the traversal.
Default value: 1.
spa_load_verify_shift (int)
Sets the maximum number of bytes to consume during pool
import to the log2 fraction of the target ARC size.
Default value: 4.
spa_slop_shift (int)
Normally, we don't allow the last 3.2%
(1/(2^spa_slop_shift)) of space in the pool to be consumed. This ensures that
we don't run the pool completely out of space, due to unaccounted changes
(e.g. to the MOS). It also limits the worst-case time to allocate space. If we
have less than this amount of free space, most ZPL operations (e.g. write,
create) will return ENOSPC.
Default value: 5.
vdev_removal_max_span (int)
During top-level vdev removal, chunks of data are copied
from the vdev which may include free space in order to trade bandwidth for
IOPS. This parameter determines the maximum span of free space (in bytes)
which will be included as "unnecessary" data in a chunk of copied
data.
The default value here was chosen to align with
zfs_vdev_read_gap_limit, which is a similar concept when doing
regular reads (but there's no reason it has to be the same).
Default value: 32,768.
vdev_file_logical_ashift (ulong)
Logical ashift for file-based devices.
Default value: 9.
vdev_file_physical_ashift (ulong)
Physical ashift for file-based devices.
Default value: 9.
zap_iterate_prefetch (int)
If this is set, when we start iterating over a ZAP
object, zfs will prefetch the entire object (all leaf blocks). However, this
is limited by
dmu_prefetch_max.
Use 1 for on (default) and 0 for off.
zfetch_array_rd_sz (ulong)
If prefetching is enabled, disable prefetching for reads
larger than this size.
Default value: 1,048,576.
zfetch_max_distance (uint)
Max bytes to prefetch per stream.
Default value: 8,388,608 (8MB).
zfetch_max_idistance (uint)
Max bytes to prefetch indirects for per stream.
Default vaule: 67,108,864 (64MB).
zfetch_max_streams (uint)
Max number of streams per zfetch (prefetch streams per
file).
Default value: 8.
zfetch_min_sec_reap (uint)
Min time before an active prefetch stream can be
reclaimed
Default value: 2.
zfs_abd_scatter_enabled (int)
Enables ARC from using scatter/gather lists and forces
all allocations to be linear in kernel memory. Disabling can improve
performance in some code paths at the expense of fragmented kernel memory.
Default value: 1.
zfs_abd_scatter_max_order (iunt)
Maximum number of consecutive memory pages allocated in a
single block for scatter/gather lists. Default value is specified by the
kernel itself.
Default value: 10 at the time of this writing.
zfs_abd_scatter_min_size (uint)
This is the minimum allocation size that will use scatter
(page-based) ABD's. Smaller allocations will use linear ABD's.
Default value: 1536 (512B and 1KB allocations will be
linear).
zfs_arc_dnode_limit (ulong)
When the number of bytes consumed by dnodes in the ARC
exceeds this number of bytes, try to unpin some of it in response to demand
for non-metadata. This value acts as a ceiling to the amount of dnode
metadata, and defaults to 0 which indicates that a percent which is based on
zfs_arc_dnode_limit_percent of the ARC meta buffers that may be used
for dnodes.
See also zfs_arc_meta_prune which serves a similar purpose
but is used when the amount of metadata in the ARC exceeds
zfs_arc_meta_limit rather than in response to overall demand for
non-metadata.
Default value: 0.
zfs_arc_dnode_limit_percent (ulong)
Percentage that can be consumed by dnodes of ARC meta
buffers.
See also zfs_arc_dnode_limit which serves a similar purpose
but has a higher priority if set to nonzero value.
Default value: 10%.
zfs_arc_dnode_reduce_percent (ulong)
Percentage of ARC dnodes to try to scan in response to
demand for non-metadata when the number of bytes consumed by dnodes exceeds
zfs_arc_dnode_limit.
Default value: 10% of the number of dnodes in the ARC.
zfs_arc_average_blocksize (int)
The ARC's buffer hash table is sized based on the
assumption of an average block size of
zfs_arc_average_blocksize
(default 8K). This works out to roughly 1MB of hash table per 1GB of physical
memory with 8-byte pointers. For configurations with a known larger average
block size this value can be increased to reduce the memory footprint.
Default value: 8192.
zfs_arc_eviction_pct (int)
When
arc_is_overflowing(),
arc_get_data_impl() waits for this percent of the requested amount of
data to be evicted. For example, by default for every 2KB that's evicted, 1KB
of it may be "reused" by a new allocation. Since this is above 100%,
it ensures that progress is made towards getting
arc_size under
arc_c. Since this is finite, it ensures that allocations can still
happen, even during the potentially long time that
arc_size is more
than
arc_c.
Default value: 200.
zfs_arc_evict_batch_limit (int)
Number ARC headers to evict per sub-list before
proceeding to another sub-list. This batch-style operation prevents entire
sub-lists from being evicted at once but comes at a cost of additional
unlocking and locking.
Default value: 10.
zfs_arc_grow_retry (int)
If set to a non zero value, it will replace the
arc_grow_retry value with this value. The arc_grow_retry value (default 5) is
the number of seconds the ARC will wait before trying to resume growth after a
memory pressure event.
Default value: 0.
zfs_arc_lotsfree_percent (int)
Throttle I/O when free system memory drops below this
percentage of total system memory. Setting this value to 0 will disable the
throttle.
Default value: 10%.
zfs_arc_max (ulong)
Max size of ARC in bytes. If set to 0 then the max size
of ARC is determined by the amount of system memory installed. For Linux, 1/2
of system memory will be used as the limit. For FreeBSD, the larger of all
system memory - 1GB or 5/8 of system memory will be used as the limit. This
value must be at least 67108864 (64 megabytes).
This value can be changed dynamically with some caveats. It cannot
be set back to 0 while running and reducing it below the current ARC size
will not cause the ARC to shrink without memory pressure to induce
shrinking.
Default value: 0.
zfs_arc_meta_adjust_restarts (ulong)
The number of restart passes to make while scanning the
ARC attempting the free buffers in order to stay below the
zfs_arc_meta_limit. This value should not need to be tuned but is
available to facilitate performance analysis.
Default value: 4096.
zfs_arc_meta_limit (ulong)
The maximum allowed size in bytes that meta data buffers
are allowed to consume in the ARC. When this limit is reached meta data
buffers will be reclaimed even if the overall arc_c_max has not been reached.
This value defaults to 0 which indicates that a percent which is based on
zfs_arc_meta_limit_percent of the ARC may be used for meta data.
This value my be changed dynamically except that it cannot be set
back to 0 for a specific percent of the ARC; it must be set to an explicit
value.
Default value: 0.
zfs_arc_meta_limit_percent (ulong)
Percentage of ARC buffers that can be used for meta data.
See also zfs_arc_meta_limit which serves a similar purpose
but has a higher priority if set to nonzero value.
Default value: 75%.
zfs_arc_meta_min (ulong)
The minimum allowed size in bytes that meta data buffers
may consume in the ARC. This value defaults to 0 which disables a floor on the
amount of the ARC devoted meta data.
Default value: 0.
zfs_arc_meta_prune (int)
The number of dentries and inodes to be scanned looking
for entries which can be dropped. This may be required when the ARC reaches
the
zfs_arc_meta_limit because dentries and inodes can pin buffers in
the ARC. Increasing this value will cause to dentry and inode caches to be
pruned more aggressively. Setting this value to 0 will disable pruning the
inode and dentry caches.
Default value: 10,000.
zfs_arc_meta_strategy (int)
Define the strategy for ARC meta data buffer eviction
(meta reclaim strategy). A value of 0 (META_ONLY) will evict only the ARC meta
data buffers. A value of 1 (BALANCED) indicates that additional data buffers
may be evicted if that is required to in order to evict the required number of
meta data buffers.
Default value: 1.
zfs_arc_min (ulong)
Min size of ARC in bytes. If set to 0 then arc_c_min will
default to consuming the larger of 32M or 1/32 of total system memory.
Default value: 0.
zfs_arc_min_prefetch_ms (int)
Minimum time prefetched blocks are locked in the ARC,
specified in ms. A value of
0 will default to 1000 ms.
Default value: 0.
zfs_arc_min_prescient_prefetch_ms (int)
Minimum time "prescient prefetched" blocks are
locked in the ARC, specified in ms. These blocks are meant to be prefetched
fairly aggressively ahead of the code that may use them. A value of
0
will default to 6000 ms.
Default value: 0.
zfs_max_missing_tvds (int)
Number of missing top-level vdevs which will be allowed
during pool import (only in read-only mode).
Default value: 0
zfs_max_nvlist_src_size (ulong)
Maximum size in bytes allowed to be passed as
zc_nvlist_src_size for ioctls on /dev/zfs. This prevents a user from causing
the kernel to allocate an excessive amount of memory. When the limit is
exceeded, the ioctl fails with EINVAL and a description of the error is sent
to the zfs-dbgmsg log. This parameter should not need to be touched under
normal circumstances. On FreeBSD, the default is based on the system limit on
user wired memory. On Linux, the default is
128MB.
Default value: 0 (kernel decides)
zfs_multilist_num_sublists (int)
To allow more fine-grained locking, each ARC state
contains a series of lists for both data and meta data objects. Locking is
performed at the level of these "sub-lists". This parameters
controls the number of sub-lists per ARC state, and also applies to other uses
of the multilist data structure.
Default value: 4 or the number of online CPUs, whichever is
greater
zfs_arc_overflow_shift (int)
The ARC size is considered to be overflowing if it
exceeds the current ARC target size (arc_c) by a threshold determined by this
parameter. The threshold is calculated as a fraction of arc_c using the
formula "arc_c >>
zfs_arc_overflow_shift".
The default value of 8 causes the ARC to be considered to be
overflowing if it exceeds the target size by 1/256th (0.3%) of the target
size.
When the ARC is overflowing, new buffer allocations are stalled
until the reclaim thread catches up and the overflow condition no longer
exists.
Default value: 8.
zfs_arc_p_min_shift (int)
If set to a non zero value, this will update
arc_p_min_shift (default 4) with the new value. arc_p_min_shift is used to
shift of arc_c for calculating both min and max max arc_p
Default value: 0.
zfs_arc_p_dampener_disable (int)
Disable arc_p adapt dampener
Use 1 for yes (default) and 0 to disable.
zfs_arc_shrink_shift (int)
If set to a non zero value, this will update
arc_shrink_shift (default 7) with the new value.
Default value: 0.
zfs_arc_pc_percent (uint)
Percent of pagecache to reclaim arc to
This tunable allows ZFS arc to play more nicely with the kernel's
LRU pagecache. It can guarantee that the ARC size won't collapse under
scanning pressure on the pagecache, yet still allows arc to be reclaimed
down to zfs_arc_min if necessary. This value is specified as percent of
pagecache size (as measured by NR_FILE_PAGES) where that percent may exceed
100. This only operates during memory pressure/reclaim.
Default value: 0% (disabled).
zfs_arc_shrinker_limit (int)
This is a limit on how many pages the ARC shrinker makes
available for eviction in response to one page allocation attempt. Note that
in practice, the kernel's shrinker can ask us to evict up to about 4x this for
one allocation attempt.
The default limit of 10,000 (in practice, 160MB per allocation
attempt with 4K pages) limits the amount of time spent attempting to reclaim
ARC memory to less than 100ms per allocation attempt, even with a small
average compressed block size of ~8KB.
The parameter can be set to 0 (zero) to disable the limit.
This parameter only applies on Linux.
Default value: 10,000.
zfs_arc_sys_free (ulong)
The target number of bytes the ARC should leave as free
memory on the system. Defaults to the larger of 1/64 of physical memory or
512K. Setting this option to a non-zero value will override the default.
Default value: 0.
zfs_autoimport_disable (int)
Disable pool import at module load by ignoring the cache
file (typically
/etc/zfs/zpool.cache).
Use 1 for yes (default) and 0 for no.
zfs_checksum_events_per_second (uint)
Rate limit checksum events to this many per second. Note
that this should not be set below the zed thresholds (currently 10 checksums
over 10 sec) or else zed may not trigger any action.
Default value: 20
zfs_commit_timeout_pct (int)
This controls the amount of time that a ZIL block (lwb)
will remain "open" when it isn't "full", and it has a
thread waiting for it to be committed to stable storage. The timeout is scaled
based on a percentage of the last lwb latency to avoid significantly impacting
the latency of each individual transaction record (itx).
Default value: 5%.
zfs_condense_indirect_commit_entry_delay_ms (int)
Vdev indirection layer (used for device removal) sleeps
for this many milliseconds during mapping generation. Intended for use with
the test suite to throttle vdev removal speed.
Default value: 0 (no throttle).
zfs_condense_indirect_obsolete_pct (int)
Minimum percent of obsolete bytes in vdev mapping
required to attempt to condense (see
zfs_condense_indirect_vdevs_enable). Intended for use with the test
suite to facilitate triggering condensing as needed.
Default value: 25%.
zfs_condense_indirect_vdevs_enable (int)
Enable condensing indirect vdev mappings. When set to a
non-zero value, attempt to condense indirect vdev mappings if the mapping uses
more than
zfs_condense_min_mapping_bytes bytes of memory and if the
obsolete space map object uses more than
zfs_condense_max_obsolete_bytes bytes on-disk. The condensing process
is an attempt to save memory by removing obsolete mappings.
Default value: 1.
zfs_condense_max_obsolete_bytes (ulong)
Only attempt to condense indirect vdev mappings if the
on-disk size of the obsolete space map object is greater than this number of
bytes (see
fBzfs_condense_indirect_vdevs_enable).
Default value: 1,073,741,824.
zfs_condense_min_mapping_bytes (ulong)
Minimum size vdev mapping to attempt to condense (see
zfs_condense_indirect_vdevs_enable).
Default value: 131,072.
zfs_dbgmsg_enable (int)
Internally ZFS keeps a small log to facilitate debugging.
By default the log is disabled, to enable it set this option to 1. The
contents of the log can be accessed by reading the /proc/spl/kstat/zfs/dbgmsg
file. Writing 0 to this proc file clears the log.
Default value: 0.
zfs_dbgmsg_maxsize (int)
The maximum size in bytes of the internal ZFS debug log.
Default value: 4M.
zfs_dbuf_state_index (int)
This feature is currently unused. It is normally used for
controlling what reporting is available under /proc/spl/kstat/zfs.
Default value: 0.
zfs_deadman_enabled (int)
When a pool sync operation takes longer than
zfs_deadman_synctime_ms milliseconds, or when an individual I/O takes
longer than
zfs_deadman_ziotime_ms milliseconds, then the operation is
considered to be "hung". If
zfs_deadman_enabled is set then
the deadman behavior is invoked as described by the
zfs_deadman_failmode module option. By default the deadman is enabled
and configured to
wait which results in "hung" I/Os only
being logged. The deadman is automatically disabled when a pool gets
suspended.
Default value: 1.
zfs_deadman_failmode (charp)
Controls the failure behavior when the deadman detects a
"hung" I/O. Valid values are
wait,
continue, and
panic.
wait - Wait for a "hung" I/O to complete. For
each "hung" I/O a "deadman" event will be posted
describing that I/O.
continue - Attempt to recover from a "hung" I/O
by re-dispatching it to the I/O pipeline if possible.
panic - Panic the system. This can be used to facilitate an
automatic fail-over to a properly configured fail-over partner.
Default value: wait.
zfs_deadman_checktime_ms (int)
Check time in milliseconds. This defines the frequency at
which we check for hung I/O and potentially invoke the
zfs_deadman_failmode behavior.
Default value: 60,000.
zfs_deadman_synctime_ms (ulong)
Interval in milliseconds after which the deadman is
triggered and also the interval after which a pool sync operation is
considered to be "hung". Once this limit is exceeded the deadman
will be invoked every
zfs_deadman_checktime_ms milliseconds until the
pool sync completes.
Default value: 600,000.
zfs_deadman_ziotime_ms (ulong)
Interval in milliseconds after which the deadman is
triggered and an individual I/O operation is considered to be
"hung". As long as the I/O remains "hung" the deadman will
be invoked every
zfs_deadman_checktime_ms milliseconds until the I/O
completes.
Default value: 300,000.
zfs_dedup_prefetch (int)
Enable prefetching dedup-ed blks
Use 1 for yes and 0 to disable (default).
zfs_delay_min_dirty_percent (int)
Start to delay each transaction once there is this amount
of dirty data, expressed as a percentage of
zfs_dirty_data_max. This
value should be >= zfs_vdev_async_write_active_max_dirty_percent. See the
section "ZFS TRANSACTION DELAY".
Default value: 60%.
zfs_delay_scale (int)
This controls how quickly the transaction delay
approaches infinity. Larger values cause longer delays for a given amount of
dirty data.
For the smoothest delay, this value should be about 1 billion
divided by the maximum number of operations per second. This will smoothly
handle between 10x and 1/10th this number.
See the section "ZFS TRANSACTION DELAY".
Note: zfs_delay_scale * zfs_dirty_data_max must be
< 2^64.
Default value: 500,000.
zfs_disable_ivset_guid_check (int)
Disables requirement for IVset guids to be present and
match when doing a raw receive of encrypted datasets. Intended for users whose
pools were created with OpenZFS pre-release versions and now have
compatibility issues.
Default value: 0.
zfs_key_max_salt_uses (ulong)
Maximum number of uses of a single salt value before
generating a new one for encrypted datasets. The default value is also the
maximum that will be accepted.
Default value: 400,000,000.
zfs_object_mutex_size (uint)
Size of the znode hashtable used for holds.
Due to the need to hold locks on objects that may not exist yet,
kernel mutexes are not created per-object and instead a hashtable is used
where collisions will result in objects waiting when there is not actually
contention on the same object.
Default value: 64.
zfs_slow_io_events_per_second (int)
Rate limit delay and deadman zevents (which report slow
I/Os) to this many per second.
Default value: 20
zfs_unflushed_max_mem_amt (ulong)
Upper-bound limit for unflushed metadata changes to be
held by the log spacemap in memory (in bytes).
Default value: 1,073,741,824 (1GB).
zfs_unflushed_max_mem_ppm (ulong)
Percentage of the overall system memory that ZFS allows
to be used for unflushed metadata changes by the log spacemap. (value is
calculated over 1000000 for finer granularity).
Default value: 1000 (which is divided by 1000000, resulting
in the limit to be 0.1% of memory)
zfs_unflushed_log_block_max (ulong)
Describes the maximum number of log spacemap blocks
allowed for each pool. The default value of 262144 means that the space in all
the log spacemaps can add up to no more than 262144 blocks (which means 32GB
of logical space before compression and ditto blocks, assuming that blocksize
is 128k).
This tunable is important because it involves a trade-off between
import time after an unclean export and the frequency of flushing metaslabs.
The higher this number is, the more log blocks we allow when the pool is
active which means that we flush metaslabs less often and thus decrease the
number of I/Os for spacemap updates per TXG. At the same time though, that
means that in the event of an unclean export, there will be more log
spacemap blocks for us to read, inducing overhead in the import time of the
pool. The lower the number, the amount of flushing increases destroying log
blocks quicker as they become obsolete faster, which leaves less blocks to
be read during import time after a crash.
Each log spacemap block existing during pool import leads to
approximately one extra logical I/O issued. This is the reason why this
tunable is exposed in terms of blocks rather than space used.
Default value: 262144 (256K).
zfs_unflushed_log_block_min (ulong)
If the number of metaslabs is small and our incoming rate
is high, we could get into a situation that we are flushing all our metaslabs
every TXG. Thus we always allow at least this many log blocks.
Default value: 1000.
zfs_unflushed_log_block_pct (ulong)
Tunable used to determine the number of blocks that can
be used for the spacemap log, expressed as a percentage of the total number of
metaslabs in the pool.
Default value: 400 (read as 400% - meaning that the
number of log spacemap blocks are capped at 4 times the number of metaslabs
in the pool).
zfs_unlink_suspend_progress (uint)
When enabled, files will not be asynchronously removed
from the list of pending unlinks and the space they consume will be leaked.
Once this option has been disabled and the dataset is remounted, the pending
unlinks will be processed and the freed space returned to the pool. This
option is used by the test suite to facilitate testing.
Uses 0 (default) to allow progress and 1 to pause
progress.
zfs_delete_blocks (ulong)
This is the used to define a large file for the purposes
of delete. Files containing more than
zfs_delete_blocks will be deleted
asynchronously while smaller files are deleted synchronously. Decreasing this
value will reduce the time spent in an unlink(2) system call at the expense of
a longer delay before the freed space is available.
Default value: 20,480.
zfs_dirty_data_max (int)
Determines the dirty space limit in bytes. Once this
limit is exceeded, new writes are halted until space frees up. This parameter
takes precedence over
zfs_dirty_data_max_percent. See the section
"ZFS TRANSACTION DELAY".
Default value: 10% of physical RAM, capped at
zfs_dirty_data_max_max.
zfs_dirty_data_max_max (int)
Maximum allowable value of
zfs_dirty_data_max,
expressed in bytes. This limit is only enforced at module load time, and will
be ignored if
zfs_dirty_data_max is later changed. This parameter takes
precedence over
zfs_dirty_data_max_max_percent. See the section
"ZFS TRANSACTION DELAY".
Default value: 25% of physical RAM.
zfs_dirty_data_max_max_percent (int)
Maximum allowable value of
zfs_dirty_data_max,
expressed as a percentage of physical RAM. This limit is only enforced at
module load time, and will be ignored if
zfs_dirty_data_max is later
changed. The parameter
zfs_dirty_data_max_max takes precedence over
this one. See the section "ZFS TRANSACTION DELAY".
Default value: 25%.
zfs_dirty_data_max_percent (int)
Determines the dirty space limit, expressed as a
percentage of all memory. Once this limit is exceeded, new writes are halted
until space frees up. The parameter
zfs_dirty_data_max takes precedence
over this one. See the section "ZFS TRANSACTION DELAY".
Default value: 10%, subject to
zfs_dirty_data_max_max.
zfs_dirty_data_sync_percent (int)
Start syncing out a transaction group if there's at least
this much dirty data as a percentage of
zfs_dirty_data_max. This should
be less than
zfs_vdev_async_write_active_min_dirty_percent.
Default value: 20% of zfs_dirty_data_max.
zfs_fallocate_reserve_percent (uint)
Since ZFS is a copy-on-write filesystem with snapshots,
blocks cannot be preallocated for a file in order to guarantee that later
writes will not run out of space. Instead, fallocate() space preallocation
only checks that sufficient space is currently available in the pool or the
user's project quota allocation, and then creates a sparse file of the
requested size. The requested space is multiplied by
zfs_fallocate_reserve_percent to allow additional space for indirect
blocks and other internal metadata. Setting this value to 0 disables support
for fallocate(2) and returns EOPNOTSUPP for fallocate() space preallocation
again.
Default value: 110%
zfs_fletcher_4_impl (string)
Select a fletcher 4 implementation.
Supported selectors are: fastest, scalar,
sse2, ssse3, avx2, avx512f, avx512bw, and
aarch64_neon. All of the selectors except fastest and
scalar require instruction set extensions to be available and will
only appear if ZFS detects that they are present at runtime. If multiple
implementations of fletcher 4 are available, the fastest will be
chosen using a micro benchmark. Selecting scalar results in the
original, CPU based calculation, being used. Selecting any option other than
fastest and scalar results in vector instructions from the
respective CPU instruction set being used.
Default value: fastest.
zfs_free_bpobj_enabled (int)
Enable/disable the processing of the free_bpobj object.
Default value: 1.
zfs_async_block_max_blocks (ulong)
Maximum number of blocks freed in a single txg.
Default value: ULONG_MAX (unlimited).
zfs_max_async_dedup_frees (ulong)
Maximum number of dedup blocks freed in a single txg.
Default value: 100,000.
zfs_override_estimate_recordsize (ulong)
Record size calculation override for zfs send estimates.
Default value: 0.
zfs_vdev_async_read_max_active (int)
Maximum asynchronous read I/Os active to each device. See
the section "ZFS I/O SCHEDULER".
Default value: 3.
zfs_vdev_async_read_min_active (int)
Minimum asynchronous read I/Os active to each device. See
the section "ZFS I/O SCHEDULER".
Default value: 1.
zfs_vdev_async_write_active_max_dirty_percent (int)
When the pool has more than
zfs_vdev_async_write_active_max_dirty_percent dirty data, use
zfs_vdev_async_write_max_active to limit active async writes. If the
dirty data is between min and max, the active I/O limit is linearly
interpolated. See the section "ZFS I/O SCHEDULER".
Default value: 60%.
zfs_vdev_async_write_active_min_dirty_percent (int)
When the pool has less than
zfs_vdev_async_write_active_min_dirty_percent dirty data, use
zfs_vdev_async_write_min_active to limit active async writes. If the
dirty data is between min and max, the active I/O limit is linearly
interpolated. See the section "ZFS I/O SCHEDULER".
Default value: 30%.
zfs_vdev_async_write_max_active (int)
Maximum asynchronous write I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
Default value: 10.
zfs_vdev_async_write_min_active (int)
Minimum asynchronous write I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
Lower values are associated with better latency on rotational
media but poorer resilver performance. The default value of 2 was chosen as
a compromise. A value of 3 has been shown to improve resilver performance
further at a cost of further increasing latency.
Default value: 2.
zfs_vdev_initializing_max_active (int)
Maximum initializing I/Os active to each device. See the
section "ZFS I/O SCHEDULER".
Default value: 1.
zfs_vdev_initializing_min_active (int)
Minimum initializing I/Os active to each device. See the
section "ZFS I/O SCHEDULER".
Default value: 1.
zfs_vdev_max_active (int)
The maximum number of I/Os active to each device.
Ideally, this will be >= the sum of each queue's max_active. See the
section "ZFS I/O SCHEDULER".
Default value: 1,000.
zfs_vdev_rebuild_max_active (int)
Maximum sequential resilver I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
Default value: 3.
zfs_vdev_rebuild_min_active (int)
Minimum sequential resilver I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
Default value: 1.
zfs_vdev_removal_max_active (int)
Maximum removal I/Os active to each device. See the
section "ZFS I/O SCHEDULER".
Default value: 2.
zfs_vdev_removal_min_active (int)
Minimum removal I/Os active to each device. See the
section "ZFS I/O SCHEDULER".
Default value: 1.
zfs_vdev_scrub_max_active (int)
Maximum scrub I/Os active to each device. See the section
"ZFS I/O SCHEDULER".
Default value: 2.
zfs_vdev_scrub_min_active (int)
Minimum scrub I/Os active to each device. See the section
"ZFS I/O SCHEDULER".
Default value: 1.
zfs_vdev_sync_read_max_active (int)
Maximum synchronous read I/Os active to each device. See
the section "ZFS I/O SCHEDULER".
Default value: 10.
zfs_vdev_sync_read_min_active (int)
Minimum synchronous read I/Os active to each device. See
the section "ZFS I/O SCHEDULER".
Default value: 10.
zfs_vdev_sync_write_max_active (int)
Maximum synchronous write I/Os active to each device. See
the section "ZFS I/O SCHEDULER".
Default value: 10.
zfs_vdev_sync_write_min_active (int)
Minimum synchronous write I/Os active to each device. See
the section "ZFS I/O SCHEDULER".
Default value: 10.
zfs_vdev_trim_max_active (int)
Maximum trim/discard I/Os active to each device. See the
section "ZFS I/O SCHEDULER".
Default value: 2.
zfs_vdev_trim_min_active (int)
Minimum trim/discard I/Os active to each device. See the
section "ZFS I/O SCHEDULER".
Default value: 1.
zfs_vdev_nia_delay (int)
For non-interactive I/O (scrub, resilver, removal,
initialize and rebuild), the number of concurrently-active I/O's is limited to
*_min_active, unless the vdev is "idle". When there are no
interactive I/Os active (sync or async), and zfs_vdev_nia_delay I/Os have
completed since the last interactive I/O, then the vdev is considered to be
"idle", and the number of concurrently-active non-interactive I/O's
is increased to *_max_active. See the section "ZFS I/O SCHEDULER".
Default value: 5.
zfs_vdev_nia_credit (int)
Some HDDs tend to prioritize sequential I/O so high, that
concurrent random I/O latency reaches several seconds. On some HDDs it happens
even if sequential I/Os are submitted one at a time, and so setting
*_max_active to 1 does not help. To prevent non-interactive I/Os, like scrub,
from monopolizing the device no more than zfs_vdev_nia_credit I/Os can be sent
while there are outstanding incomplete interactive I/Os. This enforced wait
ensures the HDD services the interactive I/O within a reasonable amount of
time. See the section "ZFS I/O SCHEDULER".
Default value: 5.
zfs_vdev_queue_depth_pct (int)
Maximum number of queued allocations per top-level vdev
expressed as a percentage of
zfs_vdev_async_write_max_active which
allows the system to detect devices that are more capable of handling
allocations and to allocate more blocks to those devices. It allows for
dynamic allocation distribution when devices are imbalanced as fuller devices
will tend to be slower than empty devices.
See also zio_dva_throttle_enabled.
Default value: 1000%.
zfs_expire_snapshot (int)
Seconds to expire .zfs/snapshot
Default value: 300.
zfs_admin_snapshot (int)
Allow the creation, removal, or renaming of entries in
the .zfs/snapshot directory to cause the creation, destruction, or renaming of
snapshots. When enabled this functionality works both locally and over NFS
exports which have the 'no_root_squash' option set. This functionality is
disabled by default.
Use 1 for yes and 0 for no (default).
zfs_flags (int)
Set additional debugging flags. The following flags may
be bitwise-or'd together.
| Value |
Symbolic Name |
|
Description |
| 1 |
ZFS_DEBUG_DPRINTF |
|
Enable dprintf entries in the debug log. |
| 2 |
ZFS_DEBUG_DBUF_VERIFY * |
|
Enable extra dbuf verifications. |
| 4 |
ZFS_DEBUG_DNODE_VERIFY * |
|
Enable extra dnode verifications. |
| 8 |
ZFS_DEBUG_SNAPNAMES |
|
Enable snapshot name verification. |
| 16 |
ZFS_DEBUG_MODIFY |
|
Check for illegally modified ARC buffers. |
| 64 |
ZFS_DEBUG_ZIO_FREE |
|
Enable verification of block frees. |
| 128 |
ZFS_DEBUG_HISTOGRAM_VERIFY |
|
Enable extra spacemap histogram verifications. |
| 256 |
ZFS_DEBUG_METASLAB_VERIFY |
|
Verify space accounting on disk matches in-core range_trees. |
| 512 |
ZFS_DEBUG_SET_ERROR |
|
Enable SET_ERROR and dprintf entries in the debug log. |
| 1024 |
ZFS_DEBUG_INDIRECT_REMAP |
|
Verify split blocks created by device removal. |
| 2048 |
ZFS_DEBUG_TRIM |
|
Verify TRIM ranges are always within the allocatable range tree. |
| 4096 |
ZFS_DEBUG_LOG_SPACEMAP |
|
Verify that the log summary is consistent with the spacemap log |
|
and enable zfs_dbgmsgs for metaslab loading and flushing. |
* Requires debug build.
Default value: 0.
zfs_free_leak_on_eio (int)
If destroy encounters an EIO while reading metadata (e.g.
indirect blocks), space referenced by the missing metadata can not be freed.
Normally this causes the background destroy to become "stalled", as
it is unable to make forward progress. While in this stalled state, all
remaining space to free from the error-encountering filesystem is
"temporarily leaked". Set this flag to cause it to ignore the EIO,
permanently leak the space from indirect blocks that can not be read, and
continue to free everything else that it can.
The default, "stalling" behavior is useful if the
storage partially fails (i.e. some but not all i/os fail), and then later
recovers. In this case, we will be able to continue pool operations while it
is partially failed, and when it recovers, we can continue to free the
space, with no leaks. However, note that this case is actually fairly
rare.
Typically pools either (a) fail completely (but perhaps
temporarily, e.g. a top-level vdev going offline), or (b) have localized,
permanent errors (e.g. disk returns the wrong data due to bit flip or
firmware bug). In case (a), this setting does not matter because the pool
will be suspended and the sync thread will not be able to make forward
progress regardless. In case (b), because the error is permanent, the best
we can do is leak the minimum amount of space, which is what setting this
flag will do. Therefore, it is reasonable for this flag to normally be set,
but we chose the more conservative approach of not setting it, so that there
is no possibility of leaking space in the "partial temporary"
failure case.
Default value: 0.
zfs_free_min_time_ms (int)
During a
zfs destroy operation using
feature@async_destroy a minimum of this much time will be spent working
on freeing blocks per txg.
Default value: 1,000.
zfs_obsolete_min_time_ms (int)
Similar to
zfs_free_min_time_ms but for cleanup of
old indirection records for removed vdevs.
Default value: 500.
zfs_immediate_write_sz (long)
Largest data block to write to zil. Larger blocks will be
treated as if the dataset being written to had the property setting
logbias=throughput.
Default value: 32,768.
zfs_initialize_value (ulong)
Pattern written to vdev free space by
zpool
initialize.
Default value: 16,045,690,984,833,335,022
(0xdeadbeefdeadbeee).
zfs_initialize_chunk_size (ulong)
Size of writes used by
zpool initialize. This
option is used by the test suite to facilitate testing.
Default value: 1,048,576
zfs_livelist_max_entries (ulong)
The threshold size (in block pointers) at which we create
a new sub-livelist. Larger sublists are more costly from a memory perspective
but the fewer sublists there are, the lower the cost of insertion.
Default value: 500,000.
zfs_livelist_min_percent_shared (int)
If the amount of shared space between a snapshot and its
clone drops below this threshold, the clone turns off the livelist and reverts
to the old deletion method. This is in place because once a clone has been
overwritten enough livelists no long give us a benefit.
Default value: 75.
zfs_livelist_condense_new_alloc (int)
Incremented each time an extra ALLOC blkptr is added to a
livelist entry while it is being condensed. This option is used by the test
suite to track race conditions.
Default value: 0.
zfs_livelist_condense_sync_cancel (int)
Incremented each time livelist condensing is canceled
while in spa_livelist_condense_sync. This option is used by the test suite to
track race conditions.
Default value: 0.
zfs_livelist_condense_sync_pause (int)
When set, the livelist condense process pauses
indefinitely before executing the synctask - spa_livelist_condense_sync. This
option is used by the test suite to trigger race conditions.
Default value: 0.
zfs_livelist_condense_zthr_cancel (int)
Incremented each time livelist condensing is canceled
while in spa_livelist_condense_cb. This option is used by the test suite to
track race conditions.
Default value: 0.
zfs_livelist_condense_zthr_pause (int)
When set, the livelist condense process pauses
indefinitely before executing the open context condensing work in
spa_livelist_condense_cb. This option is used by the test suite to trigger
race conditions.
Default value: 0.
zfs_lua_max_instrlimit (ulong)
The maximum execution time limit that can be set for a
ZFS channel program, specified as a number of Lua instructions.
Default value: 100,000,000.
zfs_lua_max_memlimit (ulong)
The maximum memory limit that can be set for a ZFS
channel program, specified in bytes.
Default value: 104,857,600.
zfs_max_dataset_nesting (int)
The maximum depth of nested datasets. This value can be
tuned temporarily to fix existing datasets that exceed the predefined limit.
Default value: 50.
zfs_max_log_walking (ulong)
The number of past TXGs that the flushing algorithm of
the log spacemap feature uses to estimate incoming log blocks.
Default value: 5.
zfs_max_logsm_summary_length (ulong)
Maximum number of rows allowed in the summary of the
spacemap log.
Default value: 10.
zfs_max_recordsize (int)
We currently support block sizes from 512 bytes to 16MB.
The benefits of larger blocks, and thus larger I/O, need to be weighed against
the cost of COWing a giant block to modify one byte. Additionally, very large
blocks can have an impact on i/o latency, and also potentially on the memory
allocator. Therefore, we do not allow the recordsize to be set larger than
zfs_max_recordsize (default 1MB). Larger blocks can be created by changing
this tunable, and pools with larger blocks can always be imported and used,
regardless of this setting.
Default value: 1,048,576.
zfs_allow_redacted_dataset_mount (int)
Allow datasets received with redacted send/receive to be
mounted. Normally disabled because these datasets may be missing key data.
Default value: 0.
zfs_min_metaslabs_to_flush (ulong)
Minimum number of metaslabs to flush per dirty TXG
Default value: 1.
zfs_metaslab_fragmentation_threshold (int)
Allow metaslabs to keep their active state as long as
their fragmentation percentage is less than or equal to this value. An active
metaslab that exceeds this threshold will no longer keep its active status
allowing better metaslabs to be selected.
Default value: 70.
zfs_mg_fragmentation_threshold (int)
Metaslab groups are considered eligible for allocations
if their fragmentation metric (measured as a percentage) is less than or equal
to this value. If a metaslab group exceeds this threshold then it will be
skipped unless all metaslab groups within the metaslab class have also crossed
this threshold.
Default value: 95.
zfs_mg_noalloc_threshold (int)
Defines a threshold at which metaslab groups should be
eligible for allocations. The value is expressed as a percentage of free space
beyond which a metaslab group is always eligible for allocations. If a
metaslab group's free space is less than or equal to the threshold, the
allocator will avoid allocating to that group unless all groups in the pool
have reached the threshold. Once all groups have reached the threshold, all
groups are allowed to accept allocations. The default value of 0 disables the
feature and causes all metaslab groups to be eligible for allocations.
This parameter allows one to deal with pools having heavily
imbalanced vdevs such as would be the case when a new vdev has been added.
Setting the threshold to a non-zero percentage will stop allocations from
being made to vdevs that aren't filled to the specified percentage and allow
lesser filled vdevs to acquire more allocations than they otherwise would
under the old zfs_mg_alloc_failures facility.
Default value: 0.
zfs_ddt_data_is_special (int)
If enabled, ZFS will place DDT data into the special
allocation class.
Default value: 1.
zfs_user_indirect_is_special (int)
If enabled, ZFS will place user data (both file and zvol)
indirect blocks into the special allocation class.
Default value: 1.
zfs_multihost_history (int)
Historical statistics for the last N multihost updates
will be available in
/proc/spl/kstat/zfs/<pool>/multihost
Default value: 0.
zfs_multihost_interval (ulong)
Used to control the frequency of multihost writes which
are performed when the
multihost pool property is on. This is one
factor used to determine the length of the activity check during import.
The multihost write period is zfs_multihost_interval /
leaf-vdevs milliseconds. On average a multihost write will be issued for
each leaf vdev every zfs_multihost_interval milliseconds. In
practice, the observed period can vary with the I/O load and this observed
value is the delay which is stored in the uberblock.
Default value: 1000.
zfs_multihost_import_intervals (uint)
Used to control the duration of the activity test on
import. Smaller values of
zfs_multihost_import_intervals will reduce
the import time but increase the risk of failing to detect an active pool. The
total activity check time is never allowed to drop below one second.
On import the activity check waits a minimum amount of time
determined by zfs_multihost_interval *
zfs_multihost_import_intervals, or the same product computed on the host
which last had the pool imported (whichever is greater). The activity check
time may be further extended if the value of mmp delay found in the best
uberblock indicates actual multihost updates happened at longer intervals
than zfs_multihost_interval. A minimum value of 100ms is
enforced.
A value of 0 is ignored and treated as if it was set to 1.
Default value: 20.
zfs_multihost_fail_intervals (uint)
Controls the behavior of the pool when multihost write
failures or delays are detected.
When zfs_multihost_fail_intervals = 0, multihost write
failures or delays are ignored. The failures will still be reported to the
ZED which depending on its configuration may take action such as suspending
the pool or offlining a device.
When zfs_multihost_fail_intervals > 0, the pool will be
suspended if zfs_multihost_fail_intervals * zfs_multihost_interval
milliseconds pass without a successful mmp write. This guarantees the
activity test will see mmp writes if the pool is imported. A value of 1 is
ignored and treated as if it was set to 2. This is necessary to prevent the
pool from being suspended due to normal, small I/O latency variations.
Default value: 10.
zfs_no_scrub_io (int)
Set for no scrub I/O. This results in scrubs not actually
scrubbing data and simply doing a metadata crawl of the pool instead.
Use 1 for yes and 0 for no (default).
zfs_no_scrub_prefetch (int)
Set to disable block prefetching for scrubs.
Use 1 for yes and 0 for no (default).
zfs_nocacheflush (int)
Disable cache flush operations on disks when writing.
Setting this will cause pool corruption on power loss if a volatile
out-of-order write cache is enabled.
Use 1 for yes and 0 for no (default).
zfs_nopwrite_enabled (int)
Enable NOP writes
Use 1 for yes (default) and 0 to disable.
zfs_dmu_offset_next_sync (int)
Enable forcing txg sync to find holes. When enabled
forces ZFS to act like prior versions when SEEK_HOLE or SEEK_DATA flags are
used, which when a dnode is dirty causes txg's to be synced so that this data
can be found.
Use 1 for yes and 0 to disable (default).
zfs_pd_bytes_max (int)
The number of bytes which should be prefetched during a
pool traversal (eg:
zfs send or other data crawling operations)
Default value: 52,428,800.
zfs_per_txg_dirty_frees_percent (ulong)
Tunable to control percentage of dirtied indirect blocks
from frees allowed into one TXG. After this threshold is crossed, additional
frees will wait until the next TXG. A value of zero will disable this
throttle.
Default value: 5, set to 0 to disable.
zfs_prefetch_disable (int)
This tunable disables predictive prefetch. Note that it
leaves "prescient" prefetch (e.g. prefetch for zfs send) intact.
Unlike predictive prefetch, prescient prefetch never issues i/os that end up
not being needed, so it can't hurt performance.
Use 1 for yes and 0 for no (default).
zfs_qat_checksum_disable (int)
This tunable disables qat hardware acceleration for
sha256 checksums. It may be set after the zfs modules have been loaded to
initialize the qat hardware as long as support is compiled in and the qat
driver is present.
Use 1 for yes and 0 for no (default).
zfs_qat_compress_disable (int)
This tunable disables qat hardware acceleration for gzip
compression. It may be set after the zfs modules have been loaded to
initialize the qat hardware as long as support is compiled in and the qat
driver is present.
Use 1 for yes and 0 for no (default).
zfs_qat_encrypt_disable (int)
This tunable disables qat hardware acceleration for
AES-GCM encryption. It may be set after the zfs modules have been loaded to
initialize the qat hardware as long as support is compiled in and the qat
driver is present.
Use 1 for yes and 0 for no (default).
zfs_read_chunk_size (long)
Bytes to read per chunk
Default value: 1,048,576.
zfs_read_history (int)
Historical statistics for the last N reads will be
available in
/proc/spl/kstat/zfs/<pool>/reads
Default value: 0 (no data is kept).
zfs_read_history_hits (int)
Include cache hits in read history
Use 1 for yes and 0 for no (default).
zfs_rebuild_max_segment (ulong)
Maximum read segment size to issue when sequentially
resilvering a top-level vdev.
Default value: 1,048,576.
zfs_reconstruct_indirect_combinations_max (int)
If an indirect split block contains more than this many
possible unique combinations when being reconstructed, consider it too
computationally expensive to check them all. Instead, try at most
zfs_reconstruct_indirect_combinations_max randomly-selected
combinations each time the block is accessed. This allows all segment copies
to participate fairly in the reconstruction when all combinations cannot be
checked and prevents repeated use of one bad copy.
Default value: 4096.
zfs_recover (int)
Set to attempt to recover from fatal errors. This should
only be used as a last resort, as it typically results in leaked space, or
worse.
Use 1 for yes and 0 for no (default).
zfs_removal_ignore_errors (int)
Ignore hard IO errors during device removal. When set, if a device
encounters a hard IO error during the removal process the removal will not
be cancelled. This can result in a normally recoverable block becoming
permanently damaged and is not recommended. This should only be used as a
last resort when the pool cannot be returned to a healthy state prior to
removing the device.
Default value: 0.
zfs_removal_suspend_progress (int)
This is used by the test suite so that it can ensure that certain
actions happen while in the middle of a removal.
Default value: 0.
zfs_remove_max_segment (int)
The largest contiguous segment that we will attempt to allocate
when removing a device. This can be no larger than 16MB. If there is a
performance problem with attempting to allocate large blocks, consider
decreasing this.
Default value: 16,777,216 (16MB).
zfs_resilver_disable_defer (int)
Disables the
resilver_defer feature, causing an
operation that would start a resilver to restart one in progress immediately.
Default value: 0 (feature enabled).
zfs_resilver_min_time_ms (int)
Resilvers are processed by the sync thread. While
resilvering it will spend at least this much time working on a resilver
between txg flushes.
Default value: 3,000.
zfs_scan_ignore_errors (int)
If set to a nonzero value, remove the DTL (dirty time
list) upon completion of a pool scan (scrub) even if there were unrepairable
errors. It is intended to be used during pool repair or recovery to stop
resilvering when the pool is next imported.
Default value: 0.
zfs_scrub_min_time_ms (int)
Scrubs are processed by the sync thread. While scrubbing
it will spend at least this much time working on a scrub between txg flushes.
Default value: 1,000.
zfs_scan_checkpoint_intval (int)
To preserve progress across reboots the sequential scan
algorithm periodically needs to stop metadata scanning and issue all the
verifications I/Os to disk. The frequency of this flushing is determined by
the
zfs_scan_checkpoint_intval tunable.
Default value: 7200 seconds (every 2 hours).
zfs_scan_fill_weight (int)
This tunable affects how scrub and resilver I/O segments
are ordered. A higher number indicates that we care more about how filled in a
segment is, while a lower number indicates we care more about the size of the
extent without considering the gaps within a segment. This value is only
tunable upon module insertion. Changing the value afterwards will have no
affect on scrub or resilver performance.
Default value: 3.
zfs_scan_issue_strategy (int)
Determines the order that data will be verified while
scrubbing or resilvering. If set to
1, data will be verified as
sequentially as possible, given the amount of memory reserved for scrubbing
(see
zfs_scan_mem_lim_fact). This may improve scrub performance if the
pool's data is very fragmented. If set to
2, the largest
mostly-contiguous chunk of found data will be verified first. By deferring
scrubbing of small segments, we may later find adjacent data to coalesce and
increase the segment size. If set to
0, zfs will use strategy
1
during normal verification and strategy
2 while taking a checkpoint.
Default value: 0.
zfs_scan_legacy (int)
A value of 0 indicates that scrubs and resilvers will
gather metadata in memory before issuing sequential I/O. A value of 1
indicates that the legacy algorithm will be used where I/O is initiated as
soon as it is discovered. Changing this value to 0 will not affect scrubs or
resilvers that are already in progress.
Default value: 0.
zfs_scan_max_ext_gap (int)
Indicates the largest gap in bytes between scrub /
resilver I/Os that will still be considered sequential for sorting purposes.
Changing this value will not affect scrubs or resilvers that are already in
progress.
Default value: 2097152 (2 MB).
zfs_scan_mem_lim_fact (int)
Maximum fraction of RAM used for I/O sorting by
sequential scan algorithm. This tunable determines the hard limit for I/O
sorting memory usage. When the hard limit is reached we stop scanning metadata
and start issuing data verification I/O. This is done until we get below the
soft limit.
Default value: 20 which is 5% of RAM (1/20).
zfs_scan_mem_lim_soft_fact (int)
The fraction of the hard limit used to determined the
soft limit for I/O sorting by the sequential scan algorithm. When we cross
this limit from below no action is taken. When we cross this limit from above
it is because we are issuing verification I/O. In this case (unless the
metadata scan is done) we stop issuing verification I/O and start scanning
metadata again until we get to the hard limit.
Default value: 20 which is 5% of the hard limit (1/20).
zfs_scan_strict_mem_lim (int)
Enforces tight memory limits on pool scans when a
sequential scan is in progress. When disabled the memory limit may be exceeded
by fast disks.
Default value: 0.
zfs_scan_suspend_progress (int)
Freezes a scrub/resilver in progress without actually
pausing it. Intended for testing/debugging.
Default value: 0.
zfs_scan_vdev_limit (int)
Maximum amount of data that can be concurrently issued at
once for scrubs and resilvers per leaf device, given in bytes.
Default value: 41943040.
zfs_send_corrupt_data (int)
Allow sending of corrupt data (ignore read/checksum
errors when sending data)
Use 1 for yes and 0 for no (default).
zfs_send_unmodified_spill_blocks (int)
Include unmodified spill blocks in the send stream. Under
certain circumstances previous versions of ZFS could incorrectly remove the
spill block from an existing object. Including unmodified copies of the spill
blocks creates a backwards compatible stream which will recreate a spill block
if it was incorrectly removed.
Use 1 for yes (default) and 0 for no.
zfs_send_no_prefetch_queue_ff (int)
The fill fraction of the
zfs send internal queues.
The fill fraction controls the timing with which internal threads are woken
up.
Default value: 20.
zfs_send_no_prefetch_queue_length (int)
The maximum number of bytes allowed in
zfs send's
internal queues.
Default value: 1,048,576.
zfs_send_queue_ff (int)
The fill fraction of the
zfs send prefetch queue.
The fill fraction controls the timing with which internal threads are woken
up.
Default value: 20.
zfs_send_queue_length (int)
The maximum number of bytes allowed that will be
prefetched by
zfs send. This value must be at least twice the maximum
block size in use.
Default value: 16,777,216.
zfs_recv_queue_ff (int)
The fill fraction of the
zfs receive queue. The
fill fraction controls the timing with which internal threads are woken up.
Default value: 20.
zfs_recv_queue_length (int)
The maximum number of bytes allowed in the
zfs
receive queue. This value must be at least twice the maximum block size in
use.
Default value: 16,777,216.
zfs_recv_write_batch_size (int)
The maximum amount of data (in bytes) that
zfs
receive will write in one DMU transaction. This is the uncompressed size,
even when receiving a compressed send stream. This setting will not reduce the
write size below a single block. Capped at a maximum of 32MB
Default value: 1MB.
zfs_override_estimate_recordsize (ulong)
Setting this variable overrides the default logic for
estimating block sizes when doing a zfs send. The default heuristic is that
the average block size will be the current recordsize. Override this value if
most data in your dataset is not of that size and you require accurate zfs
send size estimates.
Default value: 0.
zfs_sync_pass_deferred_free (int)
Flushing of data to disk is done in passes. Defer frees
starting in this pass
Default value: 2.
zfs_spa_discard_memory_limit (int)
Maximum memory used for prefetching a checkpoint's space
map on each vdev while discarding the checkpoint.
Default value: 16,777,216.
zfs_special_class_metadata_reserve_pct (int)
Only allow small data blocks to be allocated on the
special and dedup vdev types when the available free space percentage on these
vdevs exceeds this value. This ensures reserved space is available for pool
meta data as the special vdevs approach capacity.
Default value: 25.
zfs_sync_pass_dont_compress (int)
Starting in this sync pass, we disable compression
(including of metadata). With the default setting, in practice, we don't have
this many sync passes, so this has no effect.
The original intent was that disabling compression would help the
sync passes to converge. However, in practice disabling compression
increases the average number of sync passes, because when we turn
compression off, a lot of block's size will change and thus we have to
re-allocate (not overwrite) them. It also increases the number of 128KB
allocations (e.g. for indirect blocks and spacemaps) because these will not
be compressed. The 128K allocations are especially detrimental to
performance on highly fragmented systems, which may have very few free
segments of this size, and may need to load new metaslabs to satisfy 128K
allocations.
Default value: 8.
zfs_sync_pass_rewrite (int)
Rewrite new block pointers starting in this pass
Default value: 2.
zfs_sync_taskq_batch_pct (int)
This controls the number of threads used by the
dp_sync_taskq. The default value of 75% will create a maximum of one thread
per cpu.
Default value: 75%.
zfs_trim_extent_bytes_max (uint)
Maximum size of TRIM command. Ranges larger than this
will be split in to chunks no larger than
zfs_trim_extent_bytes_max
bytes before being issued to the device.
Default value: 134,217,728.
zfs_trim_extent_bytes_min (uint)
Minimum size of TRIM commands. TRIM ranges smaller than
this will be skipped unless they're part of a larger range which was broken in
to chunks. This is done because it's common for these small TRIMs to
negatively impact overall performance. This value can be set to 0 to TRIM all
unallocated space.
Default value: 32,768.
zfs_trim_metaslab_skip (uint)
Skip uninitialized metaslabs during the TRIM process.
This option is useful for pools constructed from large thinly-provisioned
devices where TRIM operations are slow. As a pool ages an increasing fraction
of the pools metaslabs will be initialized progressively degrading the
usefulness of this option. This setting is stored when starting a manual TRIM
and will persist for the duration of the requested TRIM.
Default value: 0.
zfs_trim_queue_limit (uint)
Maximum number of queued TRIMs outstanding per leaf vdev.
The number of concurrent TRIM commands issued to the device is controlled by
the
zfs_vdev_trim_min_active and
zfs_vdev_trim_max_active module
options.
Default value: 10.
zfs_trim_txg_batch (uint)
The number of transaction groups worth of frees which
should be aggregated before TRIM operations are issued to the device. This
setting represents a trade-off between issuing larger, more efficient TRIM
operations and the delay before the recently trimmed space is available for
use by the device.
Increasing this value will allow frees to be aggregated for a
longer time. This will result is larger TRIM operations and potentially
increased memory usage. Decreasing this value will have the opposite effect.
The default value of 32 was determined to be a reasonable compromise.
Default value: 32.
zfs_txg_history (int)
Historical statistics for the last N txgs will be
available in
/proc/spl/kstat/zfs/<pool>/txgs
Default value: 0.
zfs_txg_timeout (int)
Flush dirty data to disk at least every N seconds
(maximum txg duration)
Default value: 5.
zfs_vdev_aggregate_trim (int)
Allow TRIM I/Os to be aggregated. This is normally not
helpful because the extents to be trimmed will have been already been
aggregated by the metaslab. This option is provided for debugging and
performance analysis.
Default value: 0.
zfs_vdev_aggregation_limit (int)
Max vdev I/O aggregation size
Default value: 1,048,576.
zfs_vdev_aggregation_limit_non_rotating (int)
Max vdev I/O aggregation size for non-rotating media
Default value: 131,072.
zfs_vdev_cache_bshift (int)
Shift size to inflate reads too
Default value: 16 (effectively 65536).
zfs_vdev_cache_max (int)
Inflate reads smaller than this value to meet the
zfs_vdev_cache_bshift size (default 64k).
Default value: 16384.
zfs_vdev_cache_size (int)
Total size of the per-disk cache in bytes.
Currently this feature is disabled as it has been found to not be
helpful for performance and in some cases harmful.
Default value: 0.
zfs_vdev_mirror_rotating_inc (int)
A number by which the balancing algorithm increments the
load calculation for the purpose of selecting the least busy mirror member
when an I/O immediately follows its predecessor on rotational vdevs for the
purpose of making decisions based on load.
Default value: 0.
zfs_vdev_mirror_rotating_seek_inc (int)
A number by which the balancing algorithm increments the
load calculation for the purpose of selecting the least busy mirror member
when an I/O lacks locality as defined by the
zfs_vdev_mirror_rotating_seek_offset. I/Os within this that are not
immediately following the previous I/O are incremented by half.
Default value: 5.
zfs_vdev_mirror_rotating_seek_offset (int)
The maximum distance for the last queued I/O in which the
balancing algorithm considers an I/O to have locality. See the section
"ZFS I/O SCHEDULER".
Default value: 1048576.
zfs_vdev_mirror_non_rotating_inc (int)
A number by which the balancing algorithm increments the
load calculation for the purpose of selecting the least busy mirror member on
non-rotational vdevs when I/Os do not immediately follow one another.
Default value: 0.
zfs_vdev_mirror_non_rotating_seek_inc (int)
A number by which the balancing algorithm increments the
load calculation for the purpose of selecting the least busy mirror member
when an I/O lacks locality as defined by the
zfs_vdev_mirror_rotating_seek_offset. I/Os within this that are not
immediately following the previous I/O are incremented by half.
Default value: 1.
zfs_vdev_read_gap_limit (int)
Aggregate read I/O operations if the gap on-disk between
them is within this threshold.
Default value: 32,768.
zfs_vdev_write_gap_limit (int)
Aggregate write I/O over gap
Default value: 4,096.
zfs_vdev_raidz_impl (string)
Parameter for selecting raidz parity implementation to
use.
Options marked (always) below may be selected on module load as
they are supported on all systems. The remaining options may only be set
after the module is loaded, as they are available only if the
implementations are compiled in and supported on the running system.
Once the module is loaded, the content of
/sys/module/zfs/parameters/zfs_vdev_raidz_impl will show available options
with the currently selected one enclosed in []. Possible options are:
fastest - (always) implementation selected using built-in benchmark
original - (always) original raidz implementation
scalar - (always) scalar raidz implementation
sse2 - implementation using SSE2 instruction set (64bit x86 only)
ssse3 - implementation using SSSE3 instruction set (64bit x86 only)
avx2 - implementation using AVX2 instruction set (64bit x86 only)
avx512f - implementation using AVX512F instruction set (64bit x86 only)
avx512bw - implementation using AVX512F & AVX512BW instruction sets
(64bit x86 only)
aarch64_neon - implementation using NEON (Aarch64/64 bit ARMv8 only)
aarch64_neonx2 - implementation using NEON with more unrolling (Aarch64/64
bit ARMv8 only)
powerpc_altivec - implementation using Altivec (PowerPC only)
Default value: fastest.
zfs_vdev_scheduler (charp)
DEPRECATED: This option exists for compatibility
with older user configurations. It does nothing except print a warning to the
kernel log if set.
zfs_zevent_cols (int)
When zevents are logged to the console use this as the
word wrap width.
Default value: 80.
zfs_zevent_console (int)
Log events to the console
Use 1 for yes and 0 for no (default).
zfs_zevent_len_max (int)
Max event queue length. Events in the queue can be viewed
with the
zpool events command.
Default value: 512.
zfs_zevent_retain_max (int)
Maximum recent zevent records to retain for duplicate
checking. Setting this value to zero disables duplicate detection.
Default value: 2000.
zfs_zevent_retain_expire_secs (int)
Lifespan for a recent ereport that was retained for
duplicate checking.
Default value: 900.
zfs_zil_clean_taskq_maxalloc (int)
The maximum number of taskq entries that are allowed to
be cached. When this limit is exceeded transaction records (itxs) will be
cleaned synchronously.
Default value: 1048576.
zfs_zil_clean_taskq_minalloc (int)
The number of taskq entries that are pre-populated when
the taskq is first created and are immediately available for use.
Default value: 1024.
zfs_zil_clean_taskq_nthr_pct (int)
This controls the number of threads used by the
dp_zil_clean_taskq. The default value of 100% will create a maximum of one
thread per cpu.
Default value: 100%.
zil_maxblocksize (int)
This sets the maximum block size used by the ZIL. On very
fragmented pools, lowering this (typically to 36KB) can improve performance.
Default value: 131072 (128KB).
zil_nocacheflush (int)
Disable the cache flush commands that are normally sent
to the disk(s) by the ZIL after an LWB write has completed. Setting this will
cause ZIL corruption on power loss if a volatile out-of-order write cache is
enabled.
Use 1 for yes and 0 for no (default).
zil_replay_disable (int)
Disable intent logging replay. Can be disabled for
recovery from corrupted ZIL
Use 1 for yes and 0 for no (default).
zil_slog_bulk (ulong)
Limit SLOG write size per commit executed with
synchronous priority. Any writes above that will be executed with lower
(asynchronous) priority to limit potential SLOG device abuse by single active
ZIL writer.
Default value: 786,432.
zio_deadman_log_all (int)
If non-zero, the zio deadman will produce debugging
messages (see
zfs_dbgmsg_enable) for all zios, rather than only for
leaf zios possessing a vdev. This is meant to be used by developers to gain
diagnostic information for hang conditions which don't involve a mutex or
other locking primitive; typically conditions in which a thread in the zio
pipeline is looping indefinitely.
Default value: 0.
zio_decompress_fail_fraction (int)
If non-zero, this value represents the denominator of the
probability that zfs should induce a decompression failure. For instance, for
a 5% decompression failure rate, this value should be set to 20.
Default value: 0.
zio_slow_io_ms (int)
When an I/O operation takes more than
zio_slow_io_ms milliseconds to complete is marked as a slow I/O. Each
slow I/O causes a delay zevent. Slow I/O counters can be seen with "zpool
status -s".
Default value: 30,000.
zio_dva_throttle_enabled (int)
Throttle block allocations in the I/O pipeline. This
allows for dynamic allocation distribution when devices are imbalanced. When
enabled, the maximum number of pending allocations per top-level vdev is
limited by
zfs_vdev_queue_depth_pct.
Default value: 1.
zio_requeue_io_start_cut_in_line (int)
Prioritize requeued I/O
Default value: 0.
zio_taskq_batch_pct (uint)
Percentage of online CPUs (or CPU cores, etc) which will
run a worker thread for I/O. These workers are responsible for I/O work such
as compression and checksum calculations. Fractional number of CPUs will be
rounded down.
The default value of 75 was chosen to avoid using all CPUs which
can result in latency issues and inconsistent application performance,
especially when high compression is enabled.
Default value: 75.
zvol_inhibit_dev (uint)
Do not create zvol device nodes. This may slightly
improve startup time on systems with a very large number of zvols.
Use 1 for yes and 0 for no (default).
zvol_major (uint)
Major number for zvol block devices
Default value: 230.
zvol_max_discard_blocks (ulong)
Discard (aka TRIM) operations done on zvols will be done
in batches of this many blocks, where block size is determined by the
volblocksize property of a zvol.
Default value: 16,384.
zvol_prefetch_bytes (uint)
When adding a zvol to the system prefetch
zvol_prefetch_bytes from the start and end of the volume. Prefetching
these regions of the volume is desirable because they are likely to be
accessed immediately by
blkid(8) or by the kernel scanning for a
partition table.
Default value: 131,072.
zvol_request_sync (uint)
When processing I/O requests for a zvol submit them
synchronously. This effectively limits the queue depth to 1 for each I/O
submitter. When set to 0 requests are handled asynchronously by a thread pool.
The number of requests which can be handled concurrently is controller by
zvol_threads.
Default value: 0.
zvol_threads (uint)
Max number of threads which can handle zvol I/O requests
concurrently.
Default value: 32.
zvol_volmode (uint)
Defines zvol block devices behaviour when
volmode
is set to
default. Valid values are
1 (full),
2 (dev) and
3 (none).
Default value: 1.