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ZFSPROPS(7) Miscellaneous Information Manual ZFSPROPS(7)

NAME
zfsprops -- native and user-defined properties of ZFS datasets

DESCRIPTION
Properties are divided into two types, native properties and user-de-
fined (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 prop-
erties, 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
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. Na-
tive 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 descen-
dant 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 snap-
shots, 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 al-
ways 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" accessi-
ble by this dataset. See the referenced prop-
erty. The logical space ignores the effect of
the compression and copies properties, giving a
quantity closer to the amount of data that appli-
cations see. However, it does include space con-
sumed 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 ef-
fect 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 sys-
tem 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 opera-
tion. 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 par-
tially-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 snap-
shot 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 re-
sides.

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 reserva-
tion.

The used space of a snapshot (see the "Snapshots"
section of zfsconcepts(7)) is space that is ref-
erenced 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 pre-
viously 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 refer-
enced 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 necessar-
ily guarantee that the space usage information is
updated immediately.

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 de-
stroyed (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 multi-
ple 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 in-
formation.

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 con-
sumed by a user. This property counts all ob-
jects 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 sys-
tem 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 re-
quired.

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 ad-
ditional 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 ac-
cess all projects' objects usage.

snapshots_changed Provides a mechanism to quickly determine whether
snapshot list has changed without having to mount
a dataset or iterate the snapshot list. Speci-
fies the time at which a snapshot for a dataset
was last created or deleted.

This allows us to be more efficient how often we
query snapshots. The property is persistent
across mount and unmount operations only if the
extensible_dataset feature is enabled.

volblocksize For volumes, specifies the block size of the vol-
ume. 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 cre-
ated.
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 modifi-
cations.
passthrough-x same meaning as passthrough, except that the
owner@, group@, and everyone@ ACEs inherit the ex-
ecute 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 repre-
senting 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 direc-
tory, 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 cur-
rent 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 plat-
forms. 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 conse-
quence, 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 sim-
ilar to setting the mountpoint property to none, except that the
dataset still has a normal mountpoint property, which can be inher-
ited. 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 ex-
plicitly. 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|blake3
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 de-
vice 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, edonr, and blake3 checksum algorithms require en-
abling the appropriate features on the pool.

Please see zpool-features(7) for more information on these algo-
rithms.

Changing this property affects only newly-written data.

When set to on (the default), indicates that the current default com-
pression 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 [1-10, 20, 30, , 100, 500, 1000] which maps
to a negative zstd level. The lower the level the faster the com-
pression -- 1000 provides the fastest compression and lowest compres-
sion 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, 8 KiB
blocks on disks with 4 KiB 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|blake3[,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 ef-
fect 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 algo-
rithm.

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 attrib-
utes. This may be applicable to SELinux-enabled systems, Lustre
servers, and Samba servers, for example. Literal values are sup-
ported 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.

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, 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"
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 prop-
erty). 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 de-
fault for commands such as zfs load-key and zfs mount -l. This prop-
erty 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 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 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 ab-
solute 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 envi-
ronment 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 certifi-
cate 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 key-
format of passphrase is selected. The goal of PBKDF2 is to signifi-
cantly 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 func-
tion 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 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 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 512 up to 1048576 (1
MiB). 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 allo-
cation 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. In addition, any shared file systems
are unshared and shared in the new location.

When the mountpoint property is set with zfs set -u , the mountpoint
property is updated but dataset is not mounted or unmounted and re-
mains as it was before.

nbmand=on|off
Controls whether the file system should be mounted with nbmand
(Non-blocking mandatory locks). Changes to this property only take
effect when the file system is umounted and remounted. This was only
supported by Linux prior to 5.15, and was buggy there, and is not
supported by FreeBSD. On Solaris it's used for SMB clients.

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 sys-
tems 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 an-
cestor'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 in-
formation 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 privi-
lege 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 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 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 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 ac-
cess 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 ad-
versely affect performance.

The size specified must be a power of two greater than or equal to
512 B and less than or equal to 128 KiB. If the large_blocks feature
is enabled on the pool, the size may be up to 1 MiB. See
zpool-features(7) for details on ZFS feature flags.

Changing the file system's recordsize affects only files created af-
terward; existing files are unaffected.

This property can also be referred to by its shortened column name,
recsize.

redundant_metadata=all|most|some|none
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 addi-
tion 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 sin-
gle 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 1000 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.

When set to some, ZFS stores an extra copy of only critical metadata.
This can improve file create performance since less metadata needs to
be written. If a single on-disk block is corrupt, at worst a single
user file can be lost.

When set to none, ZFS does not store any copies of metadata redun-
dantly. If a single on-disk block is corrupt, an entire dataset can
be lost.

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 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 ac-
counted 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 up-
dated relative to the modify or change time. Access time is only up-
dated 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 on. 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 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 speci-
fied by its reservation. Reservations are accounted for in the par-
ent datasets' space used, and count against the parent datasets' quo-
tas 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.

prefetch=all|none|metadata
Controls what speculative prefetch does. If this property is set to
all, then both user data and metadata are prefetched. If this prop-
erty is set to none, then neither user data nor metadata are
prefetched. If this property is set to metadata, then only metadata
are prefetched. The default value is all.

Please note that the module parameter zfs_disable_prefetch=1 can be
used to totally disable speculative prefetch, bypassing anything this
property does.

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 auto-
matically shared and unshared with the zfs share and zfs unshare com-
mands. 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 under-
score (_) 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 un-
shared.

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 -- passwd(5)/shadow(5)-, LDAP- or smbpasswd(5)-based) by
default. This means that any additional access control (disallow
specific user specific access etc) must be done on the underlying
file system.

When the sharesmb property is updated with zfs set -u , the property
is set to desired value, but the operation to share, reshare or un-
share the the dataset is not performed.

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 un-
shared 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 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.

When the sharenfs property is updated with zfs set -u , the property
is set to desired value, but the operation to share, reshare or un-
share the the dataset is not performed.

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 la-
tency. 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 perfor-
mance 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 dan-
gerous 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 stor-
age 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 vol-
ume 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 set-
ting 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 par-
titions. 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 expo-
sition 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 oc-
cur. The default value is off. This property is not used by Open-
ZFS.

xattr=on|off|sa
Controls whether extended attributes are enabled for this file sys-
tem. Two styles of extended attributes are supported: either direc-
tory-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. Al-
though under Linux the getxattr(2) and setxattr(2) system calls limit
the maximum size to 64K. This is the most compatible style of ex-
tended 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 de-
creases the amount of disk I/O 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-at-
tribute-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 ac-
cess 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 this property
is not available on other platforms.

zoned=off|on
Controls whether the dataset is managed from a non-global zone or
namespace. See zfs-zone(8) for more information. Zoning is a Linux
feature and this property is not available on other platforms.

The following three properties cannot be changed after the file system
is created, and therefore, should be set when the file system is cre-
ated. 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 sys-
tem 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 combi-
nation 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
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 normaliza-
tion 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 au-
tomatically set to on. The default value of the normalization prop-
erty 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 in-
clude 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 op-
tions 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.

User Properties
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, 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 prop-
erty names can be at most 256 characters, and cannot begin with a dash
("-").

When making programmatic use of user properties, it is strongly sug-
gested 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
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 de-
fined in any parent dataset, it is removed entirely. Property values
are limited to 8192 bytes.

FreeBSD 13.2 August 8, 2023 ZFSPROPS(7)

NAME | DESCRIPTION

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=zfsprops&sektion=7&manpath=FreeBSD+14.2-RELEASE+and+Ports>

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