zfsprops —
native and user-defined properties of ZFS
datasets
Properties are divided into two types, native properties and user-defined (or
“user”) properties. Native properties either export internal
statistics or control ZFS behavior. In addition, native properties are either
editable or read-only. User properties have no effect on ZFS behavior, but you
can use them to annotate datasets in a way that is meaningful in your
environment. For more information about user properties, see the
User Properties section,
below.
Every dataset has a set of properties that export statistics about the dataset
as well as control various behaviors. Properties are inherited from the parent
unless overridden by the child. Some properties apply only to certain types of
datasets (file systems, volumes, or snapshots).
The values of numeric properties can be specified using human-readable suffixes
(for example,
k,
KB,
M,
Gb, and so forth,
up to
Z for zettabyte). The following are all
valid (and equal) specifications:
1536M, 1.5g, 1.50GB.
The values of non-numeric properties are case sensitive and must be lowercase,
except for
mountpoint,
sharenfs, and
sharesmb.
The following native properties consist of read-only statistics about the
dataset. These properties can be neither set, nor inherited. Native properties
apply to all dataset types unless otherwise noted.
- available
- The amount of space available to the dataset and all its children,
assuming that there is no other activity in the pool. Because space is
shared within a pool, availability can be limited by any number of
factors, including physical pool size, quotas, reservations, or other
datasets within the pool.
This property can also be referred to by its shortened column name,
avail.
- compressratio
- For non-snapshots, the compression ratio achieved for the
used space of this dataset, expressed as a
multiplier. The used property includes
descendant datasets, and, for clones, does not include the space shared
with the origin snapshot. For snapshots, the
compressratio is the same as the
refcompressratio property. Compression can be
turned on by running:
zfs
set
compression=on
dataset. The default value is
off.
- createtxg
- The transaction group (txg) in which the dataset was created. Bookmarks
have the same createtxg as the snapshot they
are initially tied to. This property is suitable for ordering a list of
snapshots, e.g. for incremental send and receive.
- creation
- The time this dataset was created.
- clones
- For snapshots, this property is a comma-separated list of filesystems or
volumes which are clones of this snapshot. The clones'
origin property is this snapshot. If the
clones property is not empty, then this
snapshot can not be destroyed (even with the
-r or
-f options). The roles of origin and
clone can be swapped by promoting the clone with the
zfs
promote command.
- defer_destroy
- This property is on if the snapshot has been
marked for deferred destroy by using the
zfs
destroy
-d command. Otherwise, the property is
off.
- encryptionroot
- For encrypted datasets, indicates where the dataset is currently
inheriting its encryption key from. Loading or unloading a key for the
encryptionroot will implicitly load / unload
the key for any inheriting datasets (see
zfs
load-key and
zfs
unload-key for details). Clones will
always share an encryption key with their origin. See the
Encryption section of
zfs-load-key(8) for details.
- filesystem_count
- The total number of filesystems and volumes that exist under this location
in the dataset tree. This value is only available when a
filesystem_limit has been set somewhere in
the tree under which the dataset resides.
- keystatus
- Indicates if an encryption key is currently loaded into ZFS. The possible
values are none,
available, and
unavailable. See
zfs
load-key and
zfs
unload-key.
- guid
- The 64 bit GUID of this dataset or bookmark which does not change over its
entire lifetime. When a snapshot is sent to another pool, the received
snapshot has the same GUID. Thus, the guid is
suitable to identify a snapshot across pools.
- logicalreferenced
- The amount of space that is “logically” accessible by this
dataset. See the referenced property. The
logical space ignores the effect of the
compression and
copies properties, giving a quantity closer
to the amount of data that applications see. However, it does include
space consumed by metadata.
This property can also be referred to by its shortened column name,
lrefer.
- logicalused
- The amount of space that is “logically” consumed by this
dataset and all its descendents. See the used
property. The logical space ignores the effect of the
compression and
copies properties, giving a quantity closer
to the amount of data that applications see. However, it does include
space consumed by metadata.
This property can also be referred to by its shortened column name,
lused.
- mounted
- For file systems, indicates whether the file system is currently mounted.
This property can be either yes or
no.
- objsetid
- A unique identifier for this dataset within the pool. Unlike the dataset's
guid, the
objsetid of a dataset is not transferred to
other pools when the snapshot is copied with a send/receive operation. The
objsetid can be reused (for a new dataset)
after the dataset is deleted.
- origin
- For cloned file systems or volumes, the snapshot from which the clone was
created. See also the clones property.
- receive_resume_token
- For filesystems or volumes which have saved partially-completed state from
zfs
receive
-s, this opaque token can be provided
to zfs
send
-t to resume and complete the
zfs
receive.
- redact_snaps
- For bookmarks, this is the list of snapshot guids the bookmark contains a
redaction list for. For snapshots, this is the list of snapshot guids the
snapshot is redacted with respect to.
- referenced
- The amount of data that is accessible by this dataset, which may or may
not be shared with other datasets in the pool. When a snapshot or clone is
created, it initially references the same amount of space as the file
system or snapshot it was created from, since its contents are identical.
This property can also be referred to by its shortened column name,
refer.
- refcompressratio
- The compression ratio achieved for the
referenced space of this dataset, expressed
as a multiplier. See also the compressratio
property.
- snapshot_count
- The total number of snapshots that exist under this location in the
dataset tree. This value is only available when a
snapshot_limit has been set somewhere in the
tree under which the dataset resides.
- type
- The type of dataset: filesystem,
volume,
snapshot, or
bookmark.
- used
- The amount of space consumed by this dataset and all its descendents. This
is the value that is checked against this dataset's quota and reservation.
The space used does not include this dataset's reservation, but does take
into account the reservations of any descendent datasets. The amount of
space that a dataset consumes from its parent, as well as the amount of
space that is freed if this dataset is recursively destroyed, is the
greater of its space used and its reservation.
The used space of a snapshot (see the
Snapshots section of
zfsconcepts(7)) is space that is referenced
exclusively by this snapshot. If this snapshot is destroyed, the amount of
used space will be freed. Space that is
shared by multiple snapshots isn't accounted for in this metric. When a
snapshot is destroyed, space that was previously shared with this snapshot
can become unique to snapshots adjacent to it, thus changing the used
space of those snapshots. The used space of the latest snapshot can also
be affected by changes in the file system. Note that the
used space of a snapshot is a subset of the
written space of the snapshot.
The amount of space used, available, or referenced does not take into
account pending changes. Pending changes are generally accounted for
within a few seconds. Committing a change to a disk using
fsync(2) or
O_SYNC does not necessarily guarantee that
the space usage information is updated immediately.
- usedby*
- The usedby* properties decompose the
used properties into the various reasons that
space is used. Specifically, used
= usedbychildren
+ usedbydataset
+
usedbyrefreservation
+ usedbysnapshots.
These properties are only available for datasets created on
zpool “version 13”
pools.
- usedbychildren
- The amount of space used by children of this dataset, which would be freed
if all the dataset's children were destroyed.
- usedbydataset
- The amount of space used by this dataset itself, which would be freed if
the dataset were destroyed (after first removing any
refreservation and destroying any necessary
snapshots or descendents).
- usedbyrefreservation
- The amount of space used by a refreservation
set on this dataset, which would be freed if the
refreservation was removed.
- usedbysnapshots
- The amount of space consumed by snapshots of this dataset. In particular,
it is the amount of space that would be freed if all of this dataset's
snapshots were destroyed. Note that this is not simply the sum of the
snapshots' used properties because space can
be shared by multiple snapshots.
- userused@user
- The amount of space consumed by the specified user in this dataset. Space
is charged to the owner of each file, as displayed by
ls
-l. The amount of space charged is
displayed by du
and ls
-s. See the
zfs
userspace command for more information.
Unprivileged users can access only their own space usage. The root user, or
a user who has been granted the userused
privilege with zfs
allow, can access everyone's usage.
The
userused@...
properties are not displayed by zfs
get all.
The user's name must be appended after the @
symbol, using one of the following forms:
- POSIX name (“joe”)
- POSIX numeric ID (“789”)
- SID name (“joe.smith@mydomain”)
- SID numeric ID (“S-1-123-456-789”)
Files created on Linux always have POSIX owners.
- userobjused@user
- The userobjused property is similar to
userused but instead it counts the number of
objects consumed by a user. This property counts all objects allocated on
behalf of the user, it may differ from the results of system tools such as
df
-i.
When the property
xattr=on is set
on a file system additional objects will be created per-file to store
extended attributes. These additional objects are reflected in the
userobjused value and are counted against the
user's userobjquota. When a file system is
configured to use
xattr=sa no
additional internal objects are normally required.
- userrefs
- This property is set to the number of user holds on this snapshot. User
holds are set by using the
zfs
hold command.
- groupused@group
- The amount of space consumed by the specified group in this dataset. Space
is charged to the group of each file, as displayed by
ls
-l. See the
userused@user
property for more information.
Unprivileged users can only access their own groups' space usage. The root
user, or a user who has been granted the
groupused privilege with
zfs
allow, can access all groups'
usage.
- groupobjused@group
- The number of objects consumed by the specified group in this dataset.
Multiple objects may be charged to the group for each file when extended
attributes are in use. See the
userobjused@user
property for more information.
Unprivileged users can only access their own groups' space usage. The root
user, or a user who has been granted the
groupobjused privilege with
zfs
allow, can access all groups'
usage.
- projectused@project
- The amount of space consumed by the specified project in this dataset.
Project is identified via the project identifier (ID) that is object-based
numeral attribute. An object can inherit the project ID from its parent
object (if the parent has the flag of inherit project ID that can be set
and changed via
chattr
-/+P or zfs
project -s) when being created.
The privileged user can set and change object's project ID via
chattr
-p or zfs
project -s anytime. Space is
charged to the project of each file, as displayed by
lsattr
-p or zfs
project. See the
userused@user
property for more information.
The root user, or a user who has been granted the
projectused privilege with
zfs allow, can access all projects'
usage.
- projectobjused@project
- The projectobjused is similar to
projectused but instead it counts the number
of objects consumed by project. When the property
xattr=on is set
on a fileset, ZFS will create additional objects per-file to store
extended attributes. These additional objects are reflected in the
projectobjused value and are counted against
the project's projectobjquota. When a
filesystem is configured to use
xattr=sa no
additional internal objects are required. See the
userobjused@user
property for more information.
The root user, or a user who has been granted the
projectobjused privilege with
zfs allow, can access all projects'
objects usage.
- volblocksize
- For volumes, specifies the block size of the volume. The
blocksize cannot be changed once the volume
has been written, so it should be set at volume creation time. The default
blocksize for volumes is 16 Kbytes. Any power
of 2 from 512 bytes to 128 Kbytes is valid.
This property can also be referred to by its shortened column name,
volblock.
- written
- The amount of space referenced by this
dataset, that was written since the previous snapshot (i.e. that is not
referenced by the previous snapshot).
- written@snapshot
- The amount of referenced space written to
this dataset since the specified snapshot. This is the space that is
referenced by this dataset but was not referenced by the specified
snapshot.
The snapshot may be specified as a short
snapshot name (just the part after the @), in
which case it will be interpreted as a snapshot in the same filesystem as
this dataset. The snapshot may be a full
snapshot name
(filesystem@snapshot),
which for clones may be a snapshot in the origin's filesystem (or the
origin of the origin's filesystem, etc.)
The following native properties can be used to change the behavior of a ZFS
dataset.
- aclinherit=discard|noallow|restricted|passthrough|passthrough-x
- Controls how ACEs are inherited when files and directories are created.
- discard
- does not inherit any ACEs.
- noallow
- only inherits inheritable ACEs that specify “deny”
permissions.
- restricted
- default, removes the write_acl and
write_owner permissions when the ACE is
inherited.
- passthrough
- inherits all inheritable ACEs without any modifications.
- passthrough-x
- same meaning as passthrough, except that
the owner@,
group@, and
everyone@ ACEs inherit the execute
permission only if the file creation mode also requests the execute
bit.
When the property value is set to passthrough,
files are created with a mode determined by the inheritable ACEs. If no
inheritable ACEs exist that affect the mode, then the mode is set in
accordance to the requested mode from the application.
The aclinherit property does not apply to POSIX
ACLs.
- aclmode=discard|groupmask|passthrough|restricted
- Controls how an ACL is modified during chmod(2) and how inherited ACEs are
modified by the file creation mode:
- discard
- default, deletes all ACEs except for
those representing the mode of the file or directory requested by
chmod(2).
- groupmask
- reduces permissions granted in all ALLOW
entries found in the ACL such that they
are no greater than the group permissions specified by
chmod(2).
- passthrough
- indicates that no changes are made to the ACL other than creating or
updating the necessary ACL entries to represent the new mode of the
file or directory.
- restricted
- will cause the chmod(2) operation to
return an error when used on any file or directory which has a
non-trivial ACL whose entries can not be represented by a mode.
chmod(2) is required to change the set
user ID, set group ID, or sticky bits on a file or directory, as they
do not have equivalent ACL entries. In order to use
chmod(2) on a file or directory with a
non-trivial ACL when aclmode is set to
restricted, you must first remove all ACL
entries which do not represent the current mode.
- acltype=off|nfsv4|posix
- Controls whether ACLs are enabled and if so what type of ACL to use. When
this property is set to a type of ACL not supported by the current
platform, the behavior is the same as if it were set to
off.
- off
- default on Linux, when a file system has the
acltype property set to off then ACLs are
disabled.
- noacl
- an alias for off
- nfsv4
- default on FreeBSD, indicates that NFSv4-style
ZFS ACLs should be used. These ACLs can be managed with the
getfacl(1) and
setfacl(1). The
nfsv4 ZFS ACL type is not yet supported
on Linux.
- posix
- indicates POSIX ACLs should be used. POSIX ACLs are specific to Linux
and are not functional on other platforms. POSIX ACLs are stored as an
extended attribute and therefore will not overwrite any existing NFSv4
ACLs which may be set.
- posixacl
- an alias for posix
To obtain the best performance when setting
posix users are strongly encouraged to set
the xattr=sa
property. This will result in the POSIX ACL being stored more efficiently
on disk. But as a consequence, all new extended attributes will only be
accessible from OpenZFS implementations which support the
xattr=sa
property. See the xattr property for more
details.
- atime=on|off
- Controls whether the access time for files is updated when they are read.
Turning this property off avoids producing write traffic when reading
files and can result in significant performance gains, though it might
confuse mailers and other similar utilities. The values
on and off are
equivalent to the atime and
noatime mount options. The default value is
on. See also
relatime below.
- canmount=on|off|noauto
- If this property is set to off, the file
system cannot be mounted, and is ignored by
zfs
mount
-a. Setting this property to
off is similar to setting the
mountpoint property to
none, except that the dataset still has a
normal mountpoint property, which can be
inherited. Setting this property to off
allows datasets to be used solely as a mechanism to inherit properties.
One example of setting
canmount=off is
to have two datasets with the same
mountpoint, so that the children of both
datasets appear in the same directory, but might have different inherited
characteristics.
When set to noauto, a dataset can only be
mounted and unmounted explicitly. The dataset is not mounted automatically
when the dataset is created or imported, nor is it mounted by the
zfs
mount
-a command or unmounted by the
zfs
unmount
-a command.
This property is not inherited.
- checksum=on|off|fletcher2|fletcher4|sha256|noparity|sha512|skein|edonr
- Controls the checksum used to verify data integrity. The default value is
on, which automatically selects an
appropriate algorithm (currently, fletcher4,
but this may change in future releases). The value
off disables integrity checking on user data.
The value noparity not only disables
integrity but also disables maintaining parity for user data. This setting
is used internally by a dump device residing on a RAID-Z pool and should
not be used by any other dataset. Disabling checksums is
NOT a recommended practice.
The sha512, skein,
and edonr checksum algorithms require
enabling the appropriate features on the pool.
Please see zpool-features(7) for more
information on these algorithms.
Changing this property affects only newly-written data.
- compression=on|off|gzip|gzip-N|lz4|lzjb|zle|zstd|zstd-N|zstd-fast|zstd-fast-N
- Controls the compression algorithm used for this dataset.
Setting compression to on indicates that the
current default compression algorithm should be used. The default balances
compression and decompression speed, with compression ratio and is
expected to work well on a wide variety of workloads. Unlike all other
settings for this property, on does not
select a fixed compression type. As new compression algorithms are added
to ZFS and enabled on a pool, the default compression algorithm may
change. The current default compression algorithm is either
lzjb or, if the
lz4_compress feature is enabled,
lz4.
The lz4 compression algorithm is a
high-performance replacement for the lzjb
algorithm. It features significantly faster compression and decompression,
as well as a moderately higher compression ratio than
lzjb, but can only be used on pools with the
lz4_compress feature set to
enabled. See
zpool-features(7) for details on ZFS feature
flags and the lz4_compress feature.
The lzjb compression algorithm is optimized for
performance while providing decent data compression.
The gzip compression algorithm uses the same
compression as the gzip(1) command. You can
specify the gzip level by using the value
gzip-N,
where N is an integer from 1 (fastest) to
9 (best compression ratio). Currently, gzip
is equivalent to gzip-6 (which is also the
default for gzip(1)).
The zstd compression algorithm provides both
high compression ratios and good performance. You can specify the
zstd level by using the value
zstd-N,
where N is an integer from 1 (fastest) to
19 (best compression ratio). zstd is
equivalent to zstd-3.
Faster speeds at the cost of the compression ratio can be requested by
setting a negative zstd level. This is done
using
zstd-fast-N,
where N is an integer in
[1-9,10,20,30,...,100,500,1000] which maps to a negative
zstd level. The lower the level the faster
the compression - 1000
provides the fastest compression and lowest compression
ratio. zstd-fast is equivalent to
zstd-fast-1.
The zle compression algorithm compresses runs
of zeros.
This property can also be referred to by its shortened column name
compress. Changing this property affects only
newly-written data.
When any setting except off is selected,
compression will explicitly check for blocks consisting of only zeroes
(the NUL byte). When a zero-filled block is detected, it is stored as a
hole and not compressed using the indicated compression algorithm.
Any block being compressed must be no larger than 7/8 of its original size
after compression, otherwise the compression will not be considered
worthwhile and the block saved uncompressed. Note that when the logical
block is less than 8 times the disk sector size this effectively reduces
the necessary compression ratio; for example, 8kB blocks on disks with 4kB
disk sectors must compress to 1/2 or less of their original size.
- context=none|SELinux-User:SElinux-Role:Selinux-Type:Sensitivity-Level
- This flag sets the SELinux context for all files in the file system under
a mount point for that file system. See
selinux(8) for more information.
- fscontext=none|SELinux-User:SElinux-Role:Selinux-Type:Sensitivity-Level
- This flag sets the SELinux context for the file system file system being
mounted. See selinux(8) for more
information.
- defcontext=none|SELinux-User:SElinux-Role:Selinux-Type:Sensitivity-Level
- This flag sets the SELinux default context for unlabeled files. See
selinux(8) for more information.
- rootcontext=none|SELinux-User:SElinux-Role:Selinux-Type:Sensitivity-Level
- This flag sets the SELinux context for the root inode of the file system.
See selinux(8) for more information.
- copies=1|2|3
- Controls the number of copies of data stored for this dataset. These
copies are in addition to any redundancy provided by the pool, for
example, mirroring or RAID-Z. The copies are stored on different disks, if
possible. The space used by multiple copies is charged to the associated
file and dataset, changing the used property
and counting against quotas and reservations.
Changing this property only affects newly-written data. Therefore, set this
property at file system creation time by using the
-o
copies=N
option.
Remember that ZFS will not import a pool with a missing top-level vdev. Do
NOT create, for example a two-disk striped
pool and set
copies=2 on
some datasets thinking you have setup redundancy for them. When a disk
fails you will not be able to import the pool and will have lost all of
your data.
Encrypted datasets may not have
copies=3
since the implementation stores some encryption metadata where the third
copy would normally be.
- devices=on|off
- Controls whether device nodes can be opened on this file system. The
default value is on. The values
on and off are
equivalent to the dev and
nodev mount options.
- dedup=off|on|verify|sha256[
,verify
]|sha512[,verify
]|skein[,verify
]|edonr,verify
- Configures deduplication for a dataset. The default value is
off. The default deduplication checksum is
sha256 (this may change in the future). When
dedup is enabled, the checksum defined here
overrides the checksum property. Setting the
value to verify has the same effect as the
setting
sha256,verify.
If set to verify, ZFS will do a byte-to-byte
comparison in case of two blocks having the same signature to make sure
the block contents are identical. Specifying
verify is mandatory for the
edonr algorithm.
Unless necessary, deduplication should not be
enabled on a system. See the
Deduplication section
of zfsconcepts(7).
- dnodesize=legacy|auto|1k|2k|4k|8k|16k
- Specifies a compatibility mode or literal value for the size of dnodes in
the file system. The default value is legacy.
Setting this property to a value other than
legacy requires the
large_dnode pool feature to
be enabled.
Consider setting dnodesize to
auto if the dataset uses the
xattr=sa
property setting and the workload makes heavy use of extended attributes.
This may be applicable to SELinux-enabled systems, Lustre servers, and
Samba servers, for example. Literal values are supported for cases where
the optimal size is known in advance and for performance testing.
Leave dnodesize set to
legacy if you need to receive a send stream
of this dataset on a pool that doesn't enable the
large_dnode feature, or if you need to import
this pool on a system that doesn't support the
large_dnode feature.
This property can also be referred to by its shortened column name,
dnsize.
- encryption=off|on|aes-128-ccm|aes-192-ccm|aes-256-ccm|aes-128-gcm|aes-192-gcm|aes-256-gcm
- Controls the encryption cipher suite (block cipher, key length, and mode)
used for this dataset. Requires the
encryption feature to be enabled on the pool.
Requires a keyformat to be set at dataset
creation time.
Selecting
encryption=on
when creating a dataset indicates that the default encryption suite will
be selected, which is currently aes-256-gcm.
In order to provide consistent data protection, encryption must be
specified at dataset creation time and it cannot be changed afterwards.
For more details and caveats about encryption see the
Encryption section of
zfs-load-key(8).
- keyformat=raw|hex|passphrase
- Controls what format the user's encryption key will be provided as. This
property is only set when the dataset is encrypted.
Raw keys and hex keys must be 32 bytes long (regardless of the chosen
encryption suite) and must be randomly generated. A raw key can be
generated with the following command:
#
dd
if=/dev/urandom bs=32 count=1
of=/path/to/output/key
Passphrases must be between 8 and 512 bytes long and will be processed
through PBKDF2 before being used (see the
pbkdf2iters property). Even though the
encryption suite cannot be changed after dataset creation, the keyformat
can be with zfs
change-key.
- keylocation=prompt|file:///absolute/file/path|https://address|http://address
- Controls where the user's encryption key will be loaded from by default
for commands such as
zfs
load-key and
zfs
mount
-l. This property is only set for
encrypted datasets which are encryption roots. If unspecified, the default
is prompt.
Even though the encryption suite cannot be changed after dataset creation,
the keylocation can be with either zfs
set or
zfs
change-key. If
prompt is selected ZFS will ask for the key
at the command prompt when it is required to access the encrypted data
(see zfs
load-key for details). This setting
will also allow the key to be passed in via the standard input stream, but
users should be careful not to place keys which should be kept secret on
the command line. If a file URI is selected, the key will be loaded from
the specified absolute file path. If an HTTPS or HTTP URL is selected, it
will be GETted using fetch(3), libcurl, or
nothing, depending on compile-time configuration and run-time
availability. The SSL_CA_CERT_FILE
environment variable can be set to set the location of the concatenated
certificate store. The SSL_CA_CERT_PATH
environment variable can be set to override the location of the directory
containing the certificate authority bundle. The
SSL_CLIENT_CERT_FILE and
SSL_CLIENT_KEY_FILE environment variables can
be set to configure the path to the client certificate and its key.
- pbkdf2iters=iterations
- Controls the number of PBKDF2 iterations that a
passphrase encryption key should be run
through when processing it into an encryption key. This property is only
defined when encryption is enabled and a keyformat of
passphrase is selected. The goal of PBKDF2 is
to significantly increase the computational difficulty needed to brute
force a user's passphrase. This is accomplished by forcing the attacker to
run each passphrase through a computationally expensive hashing function
many times before they arrive at the resulting key. A user who actually
knows the passphrase will only have to pay this cost once. As CPUs become
better at processing, this number should be raised to ensure that a brute
force attack is still not possible. The current default is
350000 and the minimum is
100000. This property may be changed with
zfs
change-key.
- exec=on|off
- Controls whether processes can be executed from within this file system.
The default value is on. The values
on and off are
equivalent to the exec and
noexec mount options.
- filesystem_limit=count|none
- Limits the number of filesystems and volumes that can exist under this
point in the dataset tree. The limit is not enforced if the user is
allowed to change the limit. Setting a
filesystem_limit to
on a descendent of a filesystem that already
has a filesystem_limit does not override the
ancestor's filesystem_limit, but rather
imposes an additional limit. This feature must be enabled to be used (see
zpool-features(7)).
- special_small_blocks=size
- This value represents the threshold block size for including small file
blocks into the special allocation class. Blocks smaller than or equal to
this value will be assigned to the special allocation class while greater
blocks will be assigned to the regular class. Valid values are zero or a
power of two from 512B up to 1M. The default size is 0 which means no
small file blocks will be allocated in the special class.
Before setting this property, a special class vdev must be added to the
pool. See zpoolconcepts(7) for more details
on the special allocation class.
- mountpoint=path|none|legacy
- Controls the mount point used for this file system. See the
Mount Points section of
zfsconcepts(7) for more information on how
this property is used.
When the mountpoint property is changed for a
file system, the file system and any children that inherit the mount point
are unmounted. If the new value is legacy,
then they remain unmounted. Otherwise, they are automatically remounted in
the new location if the property was previously
legacy or none,
or if they were mounted before the property was changed. In addition, any
shared file systems are unshared and shared in the new location.
- nbmand=on|off
- Controls whether the file system should be mounted with
nbmand (Non-blocking mandatory locks). This
is used for SMB clients. Changes to this property only take effect when
the file system is umounted and remounted. Support for these locks is
scarce and not described by POSIX.
- overlay=on|off
- Allow mounting on a busy directory or a directory which already contains
files or directories. This is the default mount behavior for Linux and
FreeBSD file systems. On these platforms the
property is on by default. Set to
off to disable overlay mounts for consistency
with OpenZFS on other platforms.
- primarycache=all|none|metadata
- Controls what is cached in the primary cache (ARC). If this property is
set to all, then both user data and metadata
is cached. If this property is set to none,
then neither user data nor metadata is cached. If this property is set to
metadata, then only metadata is cached. The
default value is all.
- quota=size|none
- Limits the amount of space a dataset and its descendents can consume. This
property enforces a hard limit on the amount of space used. This includes
all space consumed by descendents, including file systems and snapshots.
Setting a quota on a descendent of a dataset that already has a quota does
not override the ancestor's quota, but rather imposes an additional limit.
Quotas cannot be set on volumes, as the volsize
property acts as an implicit quota.
- snapshot_limit=count|none
- Limits the number of snapshots that can be created on a dataset and its
descendents. Setting a snapshot_limit on a
descendent of a dataset that already has a
snapshot_limit does not override the
ancestor's snapshot_limit, but rather imposes
an additional limit. The limit is not enforced if the user is allowed to
change the limit. For example, this means that recursive snapshots taken
from the global zone are counted against each delegated dataset within a
zone. This feature must be enabled to be used (see
zpool-features(7)).
- userquota@user=size|none
- Limits the amount of space consumed by the specified user. User space
consumption is identified by the
userspace@user
property.
Enforcement of user quotas may be delayed by several seconds. This delay
means that a user might exceed their quota before the system notices that
they are over quota and begins to refuse additional writes with the
EDQUOT error message. See the
zfs
userspace command for more information.
Unprivileged users can only access their own groups' space usage. The root
user, or a user who has been granted the
userquota privilege with
zfs
allow, can get and set everyone's
quota.
This property is not available on volumes, on file systems before version 4,
or on pools before version 15. The
userquota@...
properties are not displayed by zfs
get all.
The user's name must be appended after the @
symbol, using one of the following forms:
- POSIX name (“joe”)
- POSIX numeric ID (“789”)
- SID name (“joe.smith@mydomain”)
- SID numeric ID (“S-1-123-456-789”)
Files created on Linux always have POSIX owners.
- userobjquota@user=size|none
- The userobjquota is similar to
userquota but it limits the number of objects
a user can create. Please refer to
userobjused for more information about how
objects are counted.
- groupquota@group=size|none
- Limits the amount of space consumed by the specified group. Group space
consumption is identified by the
groupused@group
property.
Unprivileged users can access only their own groups' space usage. The root
user, or a user who has been granted the
groupquota privilege with
zfs
allow, can get and set all groups'
quotas.
- groupobjquota@group=size|none
- The groupobjquota is similar to
groupquota but it limits number of objects a
group can consume. Please refer to
userobjused for more information about how
objects are counted.
- projectquota@project=size|none
- Limits the amount of space consumed by the specified project. Project
space consumption is identified by the
projectused@project
property. Please refer to projectused for
more information about how project is identified and set/changed.
The root user, or a user who has been granted the
projectquota privilege with
zfs allow, can access all projects'
quota.
- projectobjquota@project=size|none
- The projectobjquota is similar to
projectquota but it limits number of objects
a project can consume. Please refer to
userobjused for more information about how
objects are counted.
- readonly=on|off
- Controls whether this dataset can be modified. The default value is
off. The values
on and off are
equivalent to the ro and
rw mount options.
This property can also be referred to by its shortened column name,
rdonly.
- recordsize=size
- Specifies a suggested block size for files in the file system. This
property is designed solely for use with database workloads that access
files in fixed-size records. ZFS automatically tunes block sizes according
to internal algorithms optimized for typical access patterns.
For databases that create very large files but access them in small random
chunks, these algorithms may be suboptimal. Specifying a
recordsize greater than or equal to the
record size of the database can result in significant performance gains.
Use of this property for general purpose file systems is strongly
discouraged, and may adversely affect performance.
The size specified must be a power of two greater than or equal to
512B and less than or equal to
128kB. If the
large_blocks feature is enabled on the pool,
the size may be up to 1MB. See
zpool-features(7) for details on ZFS feature
flags.
Changing the file system's recordsize affects
only files created afterward; existing files are unaffected.
This property can also be referred to by its shortened column name,
recsize.
- redundant_metadata=all|most
- Controls what types of metadata are stored redundantly. ZFS stores an
extra copy of metadata, so that if a single block is corrupted, the amount
of user data lost is limited. This extra copy is in addition to any
redundancy provided at the pool level (e.g. by mirroring or RAID-Z), and
is in addition to an extra copy specified by the
copies property (up to a total of 3 copies).
For example if the pool is mirrored,
copies=2, and
redundant_metadata=most,
then ZFS stores 6 copies of most metadata, and 4 copies of data and some
metadata.
When set to all, ZFS stores an extra copy of
all metadata. If a single on-disk block is corrupt, at worst a single
block of user data (which is recordsize bytes
long) can be lost.
When set to most, ZFS stores an extra copy of
most types of metadata. This can improve performance of random writes,
because less metadata must be written. In practice, at worst about 100
blocks (of recordsize bytes each) of user
data can be lost if a single on-disk block is corrupt. The exact behavior
of which metadata blocks are stored redundantly may change in future
releases.
The default value is all.
- refquota=size|none
- Limits the amount of space a dataset can consume. This property enforces a
hard limit on the amount of space used. This hard limit does not include
space used by descendents, including file systems and snapshots.
- refreservation=size|none|auto
- The minimum amount of space guaranteed to a dataset, not including its
descendents. When the amount of space used is below this value, the
dataset is treated as if it were taking up the amount of space specified
by refreservation. The
refreservation reservation is accounted for
in the parent datasets' space used, and counts against the parent
datasets' quotas and reservations.
If refreservation is set, a snapshot is only
allowed if there is enough free pool space outside of this reservation to
accommodate the current number of “referenced” bytes in the
dataset.
If refreservation is set to
auto, a volume is thick provisioned (or
“not sparse”).
refreservation=auto
is only supported on volumes. See volsize in
the Native
Properties section for more information about sparse volumes.
This property can also be referred to by its shortened column name,
refreserv.
- relatime=on|off
- Controls the manner in which the access time is updated when
atime=on is set.
Turning this property on causes the access time to be updated relative to
the modify or change time. Access time is only updated if the previous
access time was earlier than the current modify or change time or if the
existing access time hasn't been updated within the past 24 hours. The
default value is off. The values
on and off are
equivalent to the relatime and
norelatime mount options.
- reservation=size|none
- The minimum amount of space guaranteed to a dataset and its descendants.
When the amount of space used is below this value, the dataset is treated
as if it were taking up the amount of space specified by its reservation.
Reservations are accounted for in the parent datasets' space used, and
count against the parent datasets' quotas and reservations.
This property can also be referred to by its shortened column name,
reserv.
- secondarycache=all|none|metadata
- Controls what is cached in the secondary cache (L2ARC). If this property
is set to all, then both user data and
metadata is cached. If this property is set to
none, then neither user data nor metadata is
cached. If this property is set to metadata,
then only metadata is cached. The default value is
all.
- setuid=on|off
- Controls whether the setuid bit is respected for the file system. The
default value is on. The values
on and off are
equivalent to the suid and
nosuid mount options.
- sharesmb=on|off|opts
- Controls whether the file system is shared by using
Samba USERSHARES and what options are to be
used. Otherwise, the file system is automatically shared and unshared with
the
zfs
share and
zfs
unshare commands. If the property is
set to on, the net(8) command is invoked to
create a USERSHARE.
Because SMB shares requires a resource name, a unique resource name is
constructed from the dataset name. The constructed name is a copy of the
dataset name except that the characters in the dataset name, which would
be invalid in the resource name, are replaced with underscore (_)
characters. Linux does not currently support additional options which
might be available on Solaris.
If the sharesmb property is set to
off, the file systems are unshared.
The share is created with the ACL (Access Control List)
"Everyone:F" ("F" stands for "full
permissions", i.e. read and write permissions) and no guest access
(which means Samba must be able to authenticate a real user, system
passwd/shadow, LDAP or smbpasswd based) by default. This means that any
additional access control (disallow specific user specific access etc)
must be done on the underlying file system.
- sharenfs=on|off|opts
- Controls whether the file system is shared via NFS, and what options are
to be used. A file system with a sharenfs
property of off is managed with the
exportfs(8) command and entries in the
/etc/exports file. Otherwise, the file
system is automatically shared and unshared with the
zfs
share and
zfs
unshare commands. If the property is
set to on, the dataset is shared using the
default options:
sec=sys,rw,crossmnt,no_subtree_check
Please note that the options are comma-separated, unlike those found in
exports(5). This is done to negate the need
for quoting, as well as to make parsing with scripts easier.
See exports(5) for the meaning of the default
options. Otherwise, the exportfs(8) command
is invoked with options equivalent to the contents of this property.
When the sharenfs property is changed for a
dataset, the dataset and any children inheriting the property are
re-shared with the new options, only if the property was previously
off, or if they were shared before the
property was changed. If the new property is
off, the file systems are unshared.
- logbias=latency|throughput
- Provide a hint to ZFS about handling of synchronous requests in this
dataset. If logbias is set to
latency (the default), ZFS will use pool log
devices (if configured) to handle the requests at low latency. If
logbias is set to
throughput, ZFS will not use configured pool
log devices. ZFS will instead optimize synchronous operations for global
pool throughput and efficient use of resources.
- snapdev=hidden|visible
- Controls whether the volume snapshot devices under
/dev/zvol/⟨pool⟩
are hidden or visible. The default value is
hidden.
- snapdir=hidden|visible
- Controls whether the .zfs directory is
hidden or visible in the root of the file system as discussed in the
Snapshots section of
zfsconcepts(7). The default value is
hidden.
- sync=standard|always|disabled
- Controls the behavior of synchronous requests (e.g. fsync, O_DSYNC).
standard is the POSIX-specified behavior of
ensuring all synchronous requests are written to stable storage and all
devices are flushed to ensure data is not cached by device controllers
(this is the default). always causes every
file system transaction to be written and flushed before its system call
returns. This has a large performance penalty.
disabled disables synchronous requests. File
system transactions are only committed to stable storage periodically.
This option will give the highest performance. However, it is very
dangerous as ZFS would be ignoring the synchronous transaction demands of
applications such as databases or NFS. Administrators should only use this
option when the risks are understood.
- version=N|current
- The on-disk version of this file system, which is independent of the pool
version. This property can only be set to later supported versions. See
the
zfs
upgrade command.
- volsize=size
- For volumes, specifies the logical size of the volume. By default,
creating a volume establishes a reservation of equal size. For storage
pools with a version number of 9 or higher, a
refreservation is set instead. Any changes to
volsize are reflected in an equivalent change
to the reservation (or refreservation). The
volsize can only be set to a multiple of
volblocksize, and cannot be zero.
The reservation is kept equal to the volume's logical size to prevent
unexpected behavior for consumers. Without the reservation, the volume
could run out of space, resulting in undefined behavior or data
corruption, depending on how the volume is used. These effects can also
occur when the volume size is changed while it is in use (particularly
when shrinking the size). Extreme care should be used when adjusting the
volume size.
Though not recommended, a “sparse volume” (also known as
“thin provisioned”) can be created by specifying the
-s option to the
zfs
create
-V command, or by changing the value of
the refreservation property (or
reservation property on pool version 8 or
earlier) after the volume has been created. A “sparse
volume” is a volume where the value of
refreservation is less than the size of the
volume plus the space required to store its metadata. Consequently, writes
to a sparse volume can fail with ENOSPC
when the pool is low on space. For a sparse volume, changes to
volsize are not reflected in the
refreservation. A volume that is not sparse
is said to be “thick provisioned”. A sparse volume can
become thick provisioned by setting
refreservation to
auto.
- volmode=default|full|geom|dev|none
- This property specifies how volumes should be exposed to the OS. Setting
it to full exposes volumes as fully fledged
block devices, providing maximal functionality. The value
geom is just an alias for
full and is kept for compatibility. Setting
it to dev hides its partitions. Volumes with
property set to none are not exposed outside
ZFS, but can be snapshotted, cloned, replicated, etc, that can be suitable
for backup purposes. Value default means that
volumes exposition is controlled by system-wide tunable
zvol_volmode, where
full, dev and
none are encoded as 1, 2 and 3 respectively.
The default value is full.
- vscan=on|off
- Controls whether regular files should be scanned for viruses when a file
is opened and closed. In addition to enabling this property, the virus
scan service must also be enabled for virus scanning to occur. The default
value is off. This property is not used by
OpenZFS.
- xattr=on|off|sa
- Controls whether extended attributes are enabled for this file system. Two
styles of extended attributes are supported: either directory based or
system attribute based.
The default value of on enables directory based
extended attributes. This style of extended attribute imposes no practical
limit on either the size or number of attributes which can be set on a
file. Although under Linux the getxattr(2)
and setxattr(2) system calls limit the
maximum size to 64K. This is the most compatible style of extended
attribute and is supported by all ZFS implementations.
System attribute based xattrs can be enabled by setting the value to
sa. The key advantage of this type of xattr
is improved performance. Storing extended attributes as system attributes
significantly decreases the amount of disk IO required. Up to 64K of data
may be stored per-file in the space reserved for system attributes. If
there is not enough space available for an extended attribute then it will
be automatically written as a directory based xattr. System attribute
based extended attributes are not accessible on platforms which do not
support the
xattr=sa
feature. OpenZFS supports
xattr=sa on both
FreeBSD and Linux.
The use of system attribute based xattrs is strongly encouraged for users of
SELinux or POSIX ACLs. Both of these features heavily rely on extended
attributes and benefit significantly from the reduced access time.
The values on and
off are equivalent to the
xattr and
noxattr mount options.
- jailed=off|on
- Controls whether the dataset is managed from a jail. See
zfs-jail(8) for more information. Jails are a
FreeBSD feature and are not relevant on other
platforms. The default value is off.
- zoned=on|off
- Controls whether the dataset is managed from a non-global zone. Zones are
a Solaris feature and are not relevant on other platforms. The default
value is off.
The following three properties cannot be changed after the file system is
created, and therefore, should be set when the file system is created. If the
properties are not set with the
zfs
create or
zpool
create commands, these properties are
inherited from the parent dataset. If the parent dataset lacks these
properties due to having been created prior to these features being supported,
the new file system will have the default values for these properties.
- casesensitivity=sensitive|insensitive|mixed
- Indicates whether the file name matching algorithm used by the file system
should be case-sensitive, case-insensitive, or allow a combination of both
styles of matching. The default value for the
casesensitivity property is
sensitive. Traditionally,
UNIX and POSIX file systems have case-sensitive
file names.
The mixed value for the
casesensitivity property indicates that the
file system can support requests for both case-sensitive and
case-insensitive matching behavior. Currently, case-insensitive matching
behavior on a file system that supports mixed behavior is limited to the
SMB server product. For more information about the
mixed value behavior, see the "ZFS
Administration Guide".
- normalization=none|formC|formD|formKC|formKD
- Indicates whether the file system should perform a
unicode normalization of file names whenever
two file names are compared, and which normalization algorithm should be
used. File names are always stored unmodified, names are normalized as
part of any comparison process. If this property is set to a legal value
other than none, and the
utf8only property was left unspecified, the
utf8only property is automatically set to
on. The default value of the
normalization property is
none. This property cannot be changed after
the file system is created.
- utf8only=on|off
- Indicates whether the file system should reject file names that include
characters that are not present in the UTF-8
character code set. If this property is explicitly set to
off, the normalization property must either
not be explicitly set or be set to none. The
default value for the utf8only property is
off. This property cannot be changed after
the file system is created.
The
casesensitivity,
normalization, and
utf8only properties are also new permissions that
can be assigned to non-privileged users by using the ZFS delegated
administration feature.
When a file system is mounted, either through
mount(8) for legacy mounts or the
zfs
mount command for normal file systems, its
mount options are set according to its properties. The correlation between
properties and mount options is as follows:
- atime
- atime/noatime
- canmount
- auto/noauto
- devices
- dev/nodev
- exec
- exec/noexec
- readonly
- ro/rw
- relatime
- relatime/norelatime
- setuid
- suid/nosuid
- xattr
- xattr/noxattr
- nbmand
- mand/nomand
- context=
- context=
- fscontext=
- fscontext=
- defcontext=
- defcontext=
- rootcontext=
- rootcontext=
In addition, these options can be set on a per-mount basis using the
-o option, without affecting the property
that is stored on disk. The values specified on the command line override the
values stored in the dataset. The
nosuid option
is an alias for
nodevices,
nosetuid.
These properties are reported as “temporary” by the
zfs get
command. If the properties are changed while the dataset is mounted, the new
setting overrides any temporary settings.
In addition to the standard native properties, ZFS supports arbitrary user
properties. User properties have no effect on ZFS behavior, but applications
or administrators can use them to annotate datasets (file systems, volumes,
and snapshots).
User property names must contain a colon
(“
:”) character to distinguish them
from native properties. They may contain lowercase letters, numbers, and the
following punctuation characters: colon
(“
:”), dash
(“
-”), period
(“
.”), and underscore
(“
_”). The expected convention is
that the property name is divided into two portions such as
module:
property,
but this namespace is not enforced by ZFS. User property names can be at most
256 characters, and cannot begin with a dash
(“
-”).
When making programmatic use of user properties, it is strongly suggested to use
a reversed DNS domain name for the
module
component of property names to reduce the chance that two
independently-developed packages use the same property name for different
purposes.
The values of user properties are arbitrary strings, are always inherited, and
are never validated. All of the commands that operate on properties
(
zfs
list,
zfs get,
zfs set,
and so forth) can be used to manipulate both native properties and user
properties. Use the
zfs
inherit command to clear a user property.
If the property is not defined in any parent dataset, it is removed entirely.
Property values are limited to 8192 bytes.