zdb —
display ZFS storage pool debugging and consistency
information
zdb |
[ -AbcdDFGhikLMNPsvXYy
]
[]
[-I
inflight-I/O-ops
]
[-o
var=value
]…
[-t
txg
]
[-U
cache
]
[-x
dumpdir
]
[poolname[ /dataset|objset-ID ] ]
[object|range… ] |
zdb |
[ -AdiPv
]
[]
[-U
cache
]
poolname[/dataset|objset-ID ]
[object|range… ] |
zdb |
-E
[-A
]
word0:word1:…:word15 |
zdb |
-m
[-AFLPXY
]
[]
[-t
txg
]
[-U
cache
]
poolname
[] |
zdb |
-r dataset
path destination |
zdb |
-R
[-A
]
[]
[-U
cache
]
poolname
vdev:offset:[lsize/ ]psize[:flags ] |
zdb |
-S
[-AP
]
[]
[-U
cache
]
poolname |
The
zdb utility displays information about a
ZFS pool useful for debugging and performs some amount of consistency
checking. It is a not a general purpose tool and options (and facilities) may
change. It is not a
fsck(8) utility.
The output of this command in general reflects the on-disk structure of a ZFS
pool, and is inherently unstable. The precise output of most invocations is
not documented, a knowledge of ZFS internals is assumed.
If the
dataset argument does not contain any
“
/” or
“
@” characters, it is interpreted
as a pool name. The root dataset can be specified as
“
pool/”.
When operating on an imported and active pool it is possible, though unlikely,
that zdb may interpret inconsistent pool data and behave erratically.
Display options:
-b,
--block-stats- Display statistics regarding the number, size (logical, physical and
allocated) and deduplication of blocks.
-c,
--checksum- Verify the checksum of all metadata blocks while printing block statistics
(see
-b).
If specified multiple times, verify the checksums of all blocks.
-C,
--config- Display information about the configuration. If specified with no other
options, instead display information about the cache file
(/etc/zfs/zpool.cache). To specify the
cache file to display, see
-U.
If specified multiple times, and a pool name is also specified display both
the cached configuration and the on-disk configuration. If specified
multiple times with -e also display the
configuration that would be used were the pool to be imported.
-d,
--datasets- Display information about datasets. Specified once, displays basic dataset
information: ID, create transaction, size, and object count. See
-N for determining if
poolname[/dataset|objset-ID
]
is to use the specified
dataset|objset-ID
as a string (dataset name) or a number (objset ID) when datasets have
numeric names.
If specified multiple times provides greater and greater verbosity.
If object IDs or object ID ranges are specified, display information about
those specific objects or ranges only.
An object ID range is specified in terms of a colon-separated tuple of the
form
⟨start⟩:⟨end⟩[:⟨flags⟩
].
The fields start and
end are integer object identifiers that
denote the upper and lower bounds of the range. An
end value of -1 specifies a range with no
upper bound. The flags field optionally
specifies a set of flags, described below, that control which object types
are dumped. By default, all object types are dumped. A minus sign (-)
negates the effect of the flag that follows it and has no effect unless
preceded by the A flag. For example, the
range 0:-1:A-d will dump all object types except for directories.
- A
- Dump all objects (this is the default)
- d
- Dump ZFS directory objects
- f
- Dump ZFS plain file objects
- m
- Dump SPA space map objects
- z
- Dump ZAP objects
- -
- Negate the effect of next flag
-D,
--dedup-stats- Display deduplication statistics, including the deduplication ratio
(dedup), compression ratio
(compress), inflation due to the zfs copies
property (copies), and an overall effective
ratio (dedup ×
compress /
copies).
-DD- Display a histogram of deduplication statistics, showing the allocated
(physically present on disk) and referenced (logically referenced in the
pool) block counts and sizes by reference count.
-DDD- Display the statistics independently for each deduplication table.
-DDDD- Dump the contents of the deduplication tables describing duplicate
blocks.
-DDDDD- Also dump the contents of the deduplication tables describing unique
blocks.
-E,
--embedded-block-pointer=word0:word1:…:word15- Decode and display block from an embedded block pointer specified by the
word arguments.
-h,
--history- Display pool history similar to
zpool
history, but include internal changes,
transaction, and dataset information.
-i,
--intent-logs- Display information about intent log (ZIL) entries relating to each
dataset. If specified multiple times, display counts of each intent log
transaction type.
-k,
--checkpointed-state- Examine the checkpointed state of the pool. Note, the on disk format of
the pool is not reverted to the checkpointed state.
-l,
--label=device- Read the vdev labels and L2ARC header from the specified device.
zdb
-l will return 0 if valid label was
found, 1 if error occurred, and 2 if no valid labels were found. The
presence of L2ARC header is indicated by a specific sequence
(L2ARC_DEV_HDR_MAGIC). If there is an accounting error in the size or the
number of L2ARC log blocks zdb
-l will return 1. Each unique
configuration is displayed only once.
-ll
device- In addition display label space usage stats. If a valid L2ARC header was
found also display the properties of log blocks used for restoring L2ARC
contents (persistent L2ARC).
-lll
device- Display every configuration, unique or not. If a valid L2ARC header was
found also display the properties of log entries in log blocks used for
restoring L2ARC contents (persistent L2ARC).
If the
-q option is also specified, don't
print the labels or the L2ARC header.
If the -u option is also specified, also
display the uberblocks on this device. Specify multiple times to increase
verbosity.
-L,
--disable-leak-tracking- Disable leak detection and the loading of space maps. By default,
zdb verifies that all non-free blocks
are referenced, which can be very expensive.
-m,
--metaslabs- Display the offset, spacemap, free space of each metaslab, all the log
spacemaps and their obsolete entry statistics.
-mm- Also display information about the on-disk free space histogram associated
with each metaslab.
-mmm- Display the maximum contiguous free space, the in-core free space
histogram, and the percentage of free space in each space map.
-mmmm- Display every spacemap record.
-M,
--metaslab-groups- Display all "normal" vdev metaslab group information - per-vdev
metaslab count, fragmentation, and free space histogram, as well as
overall pool fragmentation and histogram.
-MM- "Special" vdevs are added to -M's normal output.
-O,
--object-lookups=dataset
path- Also display information about the maximum contiguous free space and the
percentage of free space in each space map.
-MMM- Display every spacemap record.
-N- Same as
-d but force zdb to interpret
the
[dataset|objset-ID
]
in
[poolname[
/dataset|objset-ID
]
]
as a numeric objset ID.
-O
dataset path- Look up the specified path inside of the
dataset and display its metadata and
indirect blocks. Specified path must be
relative to the root of dataset. This
option can be combined with
-v for
increasing verbosity.
-r,
--copy-object=dataset
path destination- Copy the specified path inside of the
dataset to the specified destination.
Specified path must be relative to the
root of dataset. This option can be
combined with
-v for increasing
verbosity.
-R,
--read-block=poolname
vdev:offset:[lsize/
]psize[:flags
]- Read and display a block from the specified device. By default the block
is displayed as a hex dump, but see the description of the
r flag, below.
The block is specified in terms of a colon-separated tuple
vdev (an integer vdev identifier)
offset (the offset within the vdev)
size (the physical size, or logical size
/ physical size) of the block to read and, optionally,
flags (a set of flags, described below).
- b
offset
- Print block pointer at hex offset
- c
- Calculate and display checksums
- d
- Decompress the block. Set environment variable
ZDB_NO_ZLE to skip zle when
guessing.
- e
- Byte swap the block
- g
- Dump gang block header
- i
- Dump indirect block
- r
- Dump raw uninterpreted block data
- v
- Verbose output for guessing compression algorithm
-s,
--io-stats- Report statistics on
zdb I/O. Display
operation counts, bandwidth, and error counts of I/O to the pool from
zdb.
-S,
--simulate-dedup- Simulate the effects of deduplication, constructing a DDT and then display
that DDT as with
-DD.
-u,
--uberblock- Display the current uberblock.
Other options:
-A,
--ignore-assertions- Do not abort should any assertion fail.
-AA- Enable panic recovery, certain errors which would otherwise be fatal are
demoted to warnings.
-AAA- Do not abort if asserts fail and also enable panic recovery.
-e,
--exported=[-p
path
]…- Operate on an exported pool, not present in
/etc/zfs/zpool.cache. The
-p flag specifies the path under which
devices are to be searched.
-x,
--dump-blocks=dumpdir- All blocks accessed will be copied to files in the specified directory.
The blocks will be placed in sparse files whose name is the same as that
of the file or device read.
zdb can be
then run on the generated files. Note that the
-bbc flags are sufficient to access
(and thus copy) all metadata on the pool.
-F,
--automatic-rewind- Attempt to make an unreadable pool readable by trying progressively older
transactions.
-G,
--dump-debug-msg- Dump the contents of the zfs_dbgmsg buffer before exiting
zdb. zfs_dbgmsg is a buffer used by ZFS
to dump advanced debug information.
-I,
--inflight=inflight-I/O-ops- Limit the number of outstanding checksum I/O operations to the specified
value. The default value is 200. This option affects the performance of
the
-c option.
-o,
--option=var=value…- Set the given global libzpool variable to the provided value. The value
must be an unsigned 32-bit integer. Currently only little-endian systems
are supported to avoid accidentally setting the high 32 bits of 64-bit
variables.
-P,
--parseable- Print numbers in an unscaled form more amenable to parsing, e.g.
1000000 rather than
1M.
-t,
--txg=transaction- Specify the highest transaction to use when searching for uberblocks. See
also the
-u and
-l options for a means to see the
available uberblocks and their associated transaction numbers.
-U,
--cachefile=cachefile- Use a cache file other than
/etc/zfs/zpool.cache.
-v,
--verbose- Enable verbosity. Specify multiple times for increased verbosity.
-V,
--verbatim- Attempt verbatim import. This mimics the behavior of the kernel when
loading a pool from a cachefile. Only usable with
-e.
-X,
--extreme-rewind- Attempt “extreme” transaction rewind, that is attempt the
same recovery as
-F but read
transactions otherwise deemed too old.
-Y,
--all-reconstruction- Attempt all possible combinations when reconstructing indirect split
blocks. This flag disables the individual I/O deadman timer in order to
allow as much time as required for the attempted reconstruction.
-y,
--livelist- Perform validation for livelists that are being deleted. Scans through the
livelist and metaslabs, checking for duplicate entries and compares the
two, checking for potential double frees. If it encounters issues,
warnings will be printed, but the command will not necessarily fail.
Specifying a display option more than once enables verbosity for only that
option, with more occurrences enabling more verbosity.
If no options are specified, all information about the named pool will be
displayed at default verbosity.
Example 1: Display the configuration
of imported pool rpool
# zdb -C rpool
MOS Configuration:
version: 28
name: 'rpool'
…
Example 2: Display basic dataset
information about rpool
# zdb -d rpool
Dataset mos [META], ID 0, cr_txg 4, 26.9M, 1051 objects
Dataset rpool/swap [ZVOL], ID 59, cr_txg 356, 486M, 2 objects
…
Example 3: Display basic information
about object 0 in
rpool/export/home
# zdb -d rpool/export/home 0
Dataset rpool/export/home [ZPL], ID 137, cr_txg 1546, 32K, 8 objects
Object lvl iblk dblk dsize lsize %full type
0 7 16K 16K 15.0K 16K 25.00 DMU dnode
Example 4: Display the predicted
effect of enabling deduplication on
rpool
# zdb -S rpool
Simulated DDT histogram:
bucket allocated referenced
______ ______________________________ ______________________________
refcnt blocks LSIZE PSIZE DSIZE blocks LSIZE PSIZE DSIZE
------ ------ ----- ----- ----- ------ ----- ----- -----
1 694K 27.1G 15.0G 15.0G 694K 27.1G 15.0G 15.0G
2 35.0K 1.33G 699M 699M 74.7K 2.79G 1.45G 1.45G
…
dedup = 1.11, compress = 1.80, copies = 1.00, dedup * compress / copies = 2.00
zfs(8),
zpool(8)