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ZFSPROPS(8) BSD System Manager's Manual ZFSPROPS(8)

NAME
zfsprops -- Native properties and user-defined of ZFS datasets.

DESCRIPTION
Properties are divided into two types, native properties and user-defined
(or "user") properties. Native properties either export internal statis-
tics 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.

Native Properties
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 low-
ercase, 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 short-
ened 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 snap-
shots, 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 prop-
erty 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 in-
heriting 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 suit-
able 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 short-
ened 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 applica-
tions see. However, it does include space consumed
by metadata.

This property can also be referred to by its short-
ened 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) af-
ter 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 par-
tially-completed state from zfs receive -s, this
opaque token can be provided to zfs send -t to re-
sume 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 short-
ened 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 some-
where 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 reserva-
tion. 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(8)) is space that is refer-
enced exclusively by this snapshot. If this snap-
shot 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 snap-
shot 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 snap-
shot is a subset of the written space of the snap-
shot.

The amount of space used, available, or referenced
does not take into account pending changes. Pend-
ing 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 immedi-
ately.

usedby* The usedby* properties decompose the used proper-
ties 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 snap-
shots 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 subcommand 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 af-
ter the @ symbol, using one of the following forms:

o POSIX name (for example, joe)

o POSIX numeric ID (for example, 789)

o SID name (for example, joe.smith@mydomain)

o SID numeric ID (for example, 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 re-
sults 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 addi-
tional 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 vol-
ume. The blocksize cannot be changed once the vol-
ume has been written, so it should be set at volume
creation time. The default blocksize for volumes
is 8 Kbytes. Any power of 2 from 512 bytes to 128
Kbytes is valid.

This property can also be referred to by its short-
ened 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" per-
missions.

restricted default, removes the write_acl and write_owner permis-
sions 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 permis-
sion 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 re-
quested 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 per-
missions specified by chmod(2).

passthrough indicates that no changes are made to the ACL other than
creating or updating the necessary ACL entries to repre-
sent 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) commands on FreeBSD. 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 implemen-
tations 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 in-
herit 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 inher-
ited characteristics.

When set to noauto, a dataset can only be mounted and unmounted explic-
itly. 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 dis-
ables 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. FreeBSD does not support the edonr
algorithm.

Please see zpool-features(5) for more information on these algorithms.

Changing this property affects only newly-written data.

Setting compression to on indicates that the current default compres-
sion 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 de-
fault compression algorithm may change. The current default compres-
sion algorithm is either lzjb or, if the lz4_compress feature is en-
abled, lz4.

The lz4 compression algorithm is a high-performance replacement for the
lzjb algorithm. It features significantly faster compression and de-
compression, 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(5) for details on ZFS feature flags and
the lz4_compress feature.

The lzjb compression algorithm is optimized for performance while pro-
viding 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 nega-
tive 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 com-
pressed 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 consid-
ered worthwhile and the block saved uncompressed. Note that when the
logical block is less than 8 times the disk sector size this effec-
tively reduces the necessary compression ratio; for example 8k blocks
on disks with 4k 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 un-
der a mount point for that file system. See selinux(8) for more infor-
mation.

fscontext=none|SELinux_User:SElinux_Role:Selinux_Type:Sensitivity_Level
This flag sets the SELinux context for the file system file system be-
ing 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 sys-
tem. 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 ex-
ample, mirroring or RAID-Z. The copies are stored on different disks,
if possible. The space used by multiple copies is charged to the asso-
ciated 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 op-
tion.

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 fu-
ture). 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(8).

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 at-
tributes. 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 perfor-
mance 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.

Selecting encryption=on when creating a dataset indicates that the de-
fault encryption suite will be selected, which is currently
aes-256-gcm. In order to provide consistent data protection, encryp-
tion must be specified at dataset creation time and it cannot be
changed afterwards.

For more details and caveats about encryption see the Encryption sec-
tion 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 gen-
erated with the following command:

# dd if=/dev/urandom of=/path/to/output/key bs=32 count=1

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_
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 unspeci-
fied, the default is prompt.

Even though the encryption suite cannot be changed after dataset cre-
ation, 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
STDIN, 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.

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 keyfor-
mat 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 be-
come 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 sys-
tem. 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 de-
scendent of a filesystem that already has a filesystem_limit does not
override the ancestor's filesystem_limit, but rather imposes an addi-
tional limit. This feature must be enabled to be used (see
zpool-features(5)).

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 zpool(8) 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(8) for more information on how this prop-
erty 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 re-
mounted. See mount(8) for more information on nbmand mounts. This
property is not used on Linux.

overlay=on|off
Allow mounting on a busy directory or a directory which already con-
tains 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 im-
plicit 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(5)).

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 de-
lay means that a user might exceed their quota before the system no-
tices that they are over quota and begins to refuse additional writes
with the EDQUOT error message. See the zfs userspace subcommand 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 ver-
sion 4, or on pools before version 15. The userquota@... properties
are not displayed by zfs get all. The user's name must be appended af-
ter the @ symbol, using one of the following forms:

o POSIX name (for example, joe)

o POSIX numeric ID (for example, 789)

o SID name (for example, joe.smith@mydomain)

o SID numeric ID (for example, 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 infor-
mation 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 ob-
jects a group can consume. Please refer to userobjused for more infor-
mation 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 privi-
lege 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 in-
formation 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 op-
tions.

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 ac-
cording 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 gen-
eral 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 512
and less than or equal to 128 Kbytes. If the large_blocks feature is
enabled on the pool, the size may be up to 1 Mbyte. See
zpool-features(5) for details on ZFS feature flags.

Changing the file system's recordsize affects only files created after-
ward; 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 mir-
rored, 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 cor-
rupt. The exact behavior of which metadata blocks are stored redun-
dantly may change in future releases.

The default value is all.

refquota=size|none
Limits the amount of space a dataset can consume. This property en-
forces a hard limit on the amount of space used. This hard limit does
not include space used by descendents, including file systems and snap-
shots.

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 speci-
fied 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 equiva-
lent to the relatime and norelatime mount options.

reservation=size|none
The minimum amount of space guaranteed to a dataset and its descen-
dants. 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 reserva-
tions.

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 prop-
erty 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 automat-
ically 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", ie. 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 spe-
cific 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 man-
aged 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

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 op-
tions, 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 de-
vices. 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(8). 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 ver-
sions. 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 in-
stead. 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 corrup-
tion, depending on how the volume is used. These effects can also oc-
cur 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 prop-
erty (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 vol-
ume 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. Set-
ting it to full exposes volumes as fully fledged block devices, provid-
ing 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 con-
trolled by system-wide tunable zvol_volmode, where full, dev and none
are encoded as 1, 2 and 3 respectively. The default values 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 on Linux.

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 max-
imum size to 64K. This is the most compatible style of extended attri-
bute and is supported by all OpenZFS 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 de-
creases 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 auto-
matically written as a directory based xattr. System attribute based
extended attributes are not accessible on platforms which do not sup-
port the xattr=sa feature.

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 op-
tions.

jailed=off | on
Controls whether the dataset is managed from a jail. See the "Jails"
section in zfs(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 de-
fault 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 com-
mands, 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 combina-
tion 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-in-
sensitive matching behavior. Currently, case-insensitive matching be-
havior on a file system that supports mixed behavior is limited to the
SMB server product. For more information about the mixed value behav-
ior, see the "ZFS Administration Guide".

normalization=none|formC|formD|formKC|formKD
Indicates whether the file system should perform a unicode normaliza-
tion of file names whenever two file names are compared, and which nor-
malization algorithm should be used. File names are always stored un-
modified, 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.

Temporary Mount Point Properties
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:

PROPERTY MOUNT OPTION
atime atime/noatime
canmount auto/noauto
devices dev/nodev
exec exec/noexec
readonly ro/rw
relatime relatime/norelatime
setuid suid/nosuid
xattr xattr/noxattr

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 val-
ues 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.

User Properties
In addition to the standard native properties, ZFS supports arbitrary
user properties. User properties have no effect on ZFS behavior, but ap-
plications 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, num-
bers, 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 inher-
ited, and are never validated. All of the commands that operate on prop-
erties (zfs list, zfs get, zfs set, and so forth) can be used to manipu-
late 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.

BSD September 1, 2020 BSD

NAME | DESCRIPTION

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