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zfsprops.7
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zfsprops.7
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.\"
.\" CDDL HEADER START
.\"
.\" The contents of this file are subject to the terms of the
.\" Common Development and Distribution License (the "License").
.\" You may not use this file except in compliance with the License.
.\"
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
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.\" information: Portions Copyright [yyyy] [name of copyright owner]
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.\"
.\" Copyright (c) 2009 Sun Microsystems, Inc. All Rights Reserved.
.\" Copyright 2011 Joshua M. Clulow <josh@sysmgr.org>
.\" Copyright (c) 2011, 2019 by Delphix. All rights reserved.
.\" Copyright (c) 2011, Pawel Jakub Dawidek <pjd@FreeBSD.org>
.\" Copyright (c) 2012, Glen Barber <gjb@FreeBSD.org>
.\" Copyright (c) 2012, Bryan Drewery <bdrewery@FreeBSD.org>
.\" Copyright (c) 2013, Steven Hartland <smh@FreeBSD.org>
.\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
.\" Copyright (c) 2014, Joyent, Inc. All rights reserved.
.\" Copyright (c) 2014 by Adam Stevko. All rights reserved.
.\" Copyright (c) 2014 Integros [integros.com]
.\" Copyright (c) 2016 Nexenta Systems, Inc. All Rights Reserved.
.\" Copyright (c) 2014, Xin LI <delphij@FreeBSD.org>
.\" Copyright (c) 2014-2015, The FreeBSD Foundation, All Rights Reserved.
.\" Copyright 2019 Richard Laager. All rights reserved.
.\" Copyright 2018 Nexenta Systems, Inc.
.\" Copyright 2019 Joyent, Inc.
.\" Copyright (c) 2019, Kjeld Schouten-Lebbing
.\" Copyright (c) 2022 Hewlett Packard Enterprise Development LP.
.\"
.Dd August 8, 2023
.Dt ZFSPROPS 7
.Os
.
.Sh NAME
.Nm zfsprops
.Nd native and user-defined properties of ZFS datasets
.
.Sh DESCRIPTION
Properties are divided into two types, native properties and user-defined
.Po or
.Qq user
.Pc
properties.
Native properties either export internal statistics or control ZFS behavior.
In addition, native properties are either editable or read-only.
User properties have no effect on ZFS behavior, but you can use them to annotate
datasets in a way that is meaningful in your environment.
For more information about user properties, see the
.Sx User Properties
section, below.
.
.Ss 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
.Pq file systems, volumes, or snapshots .
.Pp
The values of numeric properties can be specified using human-readable suffixes
.Po for example,
.Sy k ,
.Sy KB ,
.Sy M ,
.Sy Gb ,
and so forth, up to
.Sy Z
for zettabyte
.Pc .
The following are all valid
.Pq and equal
specifications:
.Li 1536M ,
.Li 1.5g ,
.Li 1.50GB .
.Pp
The values of non-numeric properties are case sensitive and must be lowercase,
except for
.Sy mountpoint ,
.Sy sharenfs ,
and
.Sy sharesmb .
.Pp
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.
.Bl -tag -width "usedbyrefreservation"
.It Sy 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.
.Pp
This property can also be referred to by its shortened column name,
.Sy avail .
.It Sy compressratio
For non-snapshots, the compression ratio achieved for the
.Sy used
space of this dataset, expressed as a multiplier.
The
.Sy used
property includes descendant datasets, and, for clones, does not include the
space shared with the origin snapshot.
For snapshots, the
.Sy compressratio
is the same as the
.Sy refcompressratio
property.
Compression can be turned on by running:
.Nm zfs Cm set Sy compression Ns = Ns Sy on Ar dataset .
The default value is
.Sy off .
.It Sy createtxg
The transaction group (txg) in which the dataset was created.
Bookmarks have the same
.Sy createtxg
as the snapshot they are initially tied to.
This property is suitable for ordering a list of snapshots,
e.g. for incremental send and receive.
.It Sy creation
The time this dataset was created.
.It Sy clones
For snapshots, this property is a comma-separated list of filesystems or volumes
which are clones of this snapshot.
The clones'
.Sy origin
property is this snapshot.
If the
.Sy clones
property is not empty, then this snapshot can not be destroyed
.Po even with the
.Fl r
or
.Fl f
options
.Pc .
The roles of origin and clone can be swapped by promoting the clone with the
.Nm zfs Cm promote
command.
.It Sy defer_destroy
This property is
.Sy on
if the snapshot has been marked for deferred destroy by using the
.Nm zfs Cm destroy Fl d
command.
Otherwise, the property is
.Sy off .
.It Sy encryptionroot
For encrypted datasets, indicates where the dataset is currently inheriting its
encryption key from.
Loading or unloading a key for the
.Sy encryptionroot
will implicitly load / unload the key for any inheriting datasets (see
.Nm zfs Cm load-key
and
.Nm zfs Cm unload-key
for details).
Clones will always share an
encryption key with their origin.
See the
.Sx Encryption
section of
.Xr zfs-load-key 8
for details.
.It Sy 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
.Sy filesystem_limit
has been set somewhere in the tree under which the dataset resides.
.It Sy keystatus
Indicates if an encryption key is currently loaded into ZFS.
The possible values are
.Sy none ,
.Sy available ,
and
.Sy unavailable .
See
.Nm zfs Cm load-key
and
.Nm zfs Cm unload-key .
.It Sy 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
.Sy guid
is suitable to identify a snapshot across pools.
.It Sy logicalreferenced
The amount of space that is
.Qq logically
accessible by this dataset.
See the
.Sy referenced
property.
The logical space ignores the effect of the
.Sy compression
and
.Sy copies
properties, giving a quantity closer to the amount of data that applications
see.
However, it does include space consumed by metadata.
.Pp
This property can also be referred to by its shortened column name,
.Sy lrefer .
.It Sy logicalused
The amount of space that is
.Qq logically
consumed by this dataset and all its descendents.
See the
.Sy used
property.
The logical space ignores the effect of the
.Sy compression
and
.Sy copies
properties, giving a quantity closer to the amount of data that applications
see.
However, it does include space consumed by metadata.
.Pp
This property can also be referred to by its shortened column name,
.Sy lused .
.It Sy mounted
For file systems, indicates whether the file system is currently mounted.
This property can be either
.Sy yes
or
.Sy no .
.It Sy objsetid
A unique identifier for this dataset within the pool.
Unlike the dataset's
.Sy guid , No the Sy objsetid
of a dataset is not transferred to other pools when the snapshot is copied
with a send/receive operation.
The
.Sy objsetid
can be reused (for a new dataset) after the dataset is deleted.
.It Sy origin
For cloned file systems or volumes, the snapshot from which the clone was
created.
See also the
.Sy clones
property.
.It Sy receive_resume_token
For filesystems or volumes which have saved partially-completed state from
.Nm zfs Cm receive Fl s ,
this opaque token can be provided to
.Nm zfs Cm send Fl t
to resume and complete the
.Nm zfs Cm receive .
.It Sy 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.
.It Sy 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.
.Pp
This property can also be referred to by its shortened column name,
.Sy refer .
.It Sy refcompressratio
The compression ratio achieved for the
.Sy referenced
space of this dataset, expressed as a multiplier.
See also the
.Sy compressratio
property.
.It Sy snapshot_count
The total number of snapshots that exist under this location in the dataset
tree.
This value is only available when a
.Sy snapshot_limit
has been set somewhere in the tree under which the dataset resides.
.It Sy type
The type of dataset:
.Sy filesystem ,
.Sy volume ,
.Sy snapshot ,
or
.Sy bookmark .
.It Sy used
The amount of space consumed by this dataset and all its descendents.
This is the value that is checked against this dataset's quota and reservation.
The space used does not include this dataset's reservation, but does take into
account the reservations of any descendent datasets.
The amount of space that a dataset consumes from its parent, as well as the
amount of space that is freed if this dataset is recursively destroyed, is the
greater of its space used and its reservation.
.Pp
The used space of a snapshot
.Po see the
.Sx Snapshots
section of
.Xr zfsconcepts 7
.Pc
is space that is referenced exclusively by this snapshot.
If this snapshot is destroyed, the amount of
.Sy used
space will be freed.
Space that is shared by multiple snapshots isn't accounted for in this metric.
When a snapshot is destroyed, space that was previously shared with this
snapshot can become unique to snapshots adjacent to it, thus changing the used
space of those snapshots.
The used space of the latest snapshot can also be affected by changes in the
file system.
Note that the
.Sy used
space of a snapshot is a subset of the
.Sy written
space of the snapshot.
.Pp
The amount of space used, available, or referenced does not take into account
pending changes.
Pending changes are generally accounted for within a few seconds.
Committing a change to a disk using
.Xr fsync 2
or
.Sy O_SYNC
does not necessarily guarantee that the space usage information is updated
immediately.
.It Sy usedby*
The
.Sy usedby*
properties decompose the
.Sy used
properties into the various reasons that space is used.
Specifically,
.Sy used No =
.Sy usedbychildren No +
.Sy usedbydataset No +
.Sy usedbyrefreservation No +
.Sy usedbysnapshots .
These properties are only available for datasets created on
.Nm zpool
.Qo version 13 Qc
pools.
.It Sy usedbychildren
The amount of space used by children of this dataset, which would be freed if
all the dataset's children were destroyed.
.It Sy usedbydataset
The amount of space used by this dataset itself, which would be freed if the
dataset were destroyed
.Po after first removing any
.Sy refreservation
and destroying any necessary snapshots or descendents
.Pc .
.It Sy usedbyrefreservation
The amount of space used by a
.Sy refreservation
set on this dataset, which would be freed if the
.Sy refreservation
was removed.
.It Sy 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'
.Sy used
properties because space can be shared by multiple snapshots.
.It Sy userused Ns @ Ns Ar 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
.Nm ls Fl l .
The amount of space charged is displayed by
.Nm du No and Nm ls Fl s .
See the
.Nm zfs Cm userspace
command for more information.
.Pp
Unprivileged users can access only their own space usage.
The root user, or a user who has been granted the
.Sy userused
privilege with
.Nm zfs Cm allow ,
can access everyone's usage.
.Pp
The
.Sy userused Ns @ Ns Ar …
properties are not displayed by
.Nm zfs Cm get Sy all .
The user's name must be appended after the
.Sy @
symbol, using one of the following forms:
.Bl -bullet -compact -offset 4n
.It
POSIX name
.Pq Qq joe
.It
POSIX numeric ID
.Pq Qq 789
.It
SID name
.Pq Qq joe.smith@mydomain
.It
SID numeric ID
.Pq Qq S-1-123-456-789
.El
.Pp
Files created on Linux always have POSIX owners.
.It Sy userobjused Ns @ Ns Ar user
The
.Sy userobjused
property is similar to
.Sy userused
but instead it counts the number of objects consumed by a user.
This property counts all objects allocated on behalf of the user,
it may differ from the results of system tools such as
.Nm df Fl i .
.Pp
When the property
.Sy xattr Ns = Ns Sy 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
.Sy userobjused
value and are counted against the user's
.Sy userobjquota .
When a file system is configured to use
.Sy xattr Ns = Ns Sy sa
no additional internal objects are normally required.
.It Sy userrefs
This property is set to the number of user holds on this snapshot.
User holds are set by using the
.Nm zfs Cm hold
command.
.It Sy groupused Ns @ Ns Ar 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
.Nm ls Fl l .
See the
.Sy userused Ns @ Ns Ar user
property for more information.
.Pp
Unprivileged users can only access their own groups' space usage.
The root user, or a user who has been granted the
.Sy groupused
privilege with
.Nm zfs Cm allow ,
can access all groups' usage.
.It Sy groupobjused Ns @ Ns Ar 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
.Sy userobjused Ns @ Ns Ar user
property for more information.
.Pp
Unprivileged users can only access their own groups' space usage.
The root user, or a user who has been granted the
.Sy groupobjused
privilege with
.Nm zfs Cm allow ,
can access all groups' usage.
.It Sy projectused Ns @ Ns Ar 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
.Nm chattr Fl /+P
or
.Nm zfs project Fl s )
when being created.
The privileged user can set and change object's project
ID via
.Nm chattr Fl p
or
.Nm zfs project Fl s
anytime.
Space is charged to the project of each file, as displayed by
.Nm lsattr Fl p
or
.Nm zfs project .
See the
.Sy userused Ns @ Ns Ar user
property for more information.
.Pp
The root user, or a user who has been granted the
.Sy projectused
privilege with
.Nm zfs allow ,
can access all projects' usage.
.It Sy projectobjused Ns @ Ns Ar project
The
.Sy projectobjused
is similar to
.Sy projectused
but instead it counts the number of objects consumed by project.
When the property
.Sy xattr Ns = Ns Sy on
is set on a fileset, ZFS will create additional objects per-file to store
extended attributes.
These additional objects are reflected in the
.Sy projectobjused
value and are counted against the project's
.Sy projectobjquota .
When a filesystem is configured to use
.Sy xattr Ns = Ns Sy sa
no additional internal objects are required.
See the
.Sy userobjused Ns @ Ns Ar user
property for more information.
.Pp
The root user, or a user who has been granted the
.Sy projectobjused
privilege with
.Nm zfs allow ,
can access all projects' objects usage.
.It Sy snapshots_changed
Provides a mechanism to quickly determine whether snapshot list has
changed without having to mount a dataset or iterate the snapshot list.
Specifies the time at which a snapshot for a dataset was last
created or deleted.
.Pp
This allows us to be more efficient how often we query snapshots.
The property is persistent across mount and unmount operations only if the
.Sy extensible_dataset
feature is enabled.
.It Sy volblocksize
For volumes, specifies the block size of the volume.
The
.Sy blocksize
cannot be changed once the volume has been written, so it should be set at
volume creation time.
The default
.Sy blocksize
for volumes is 16 Kbytes.
Any power of 2 from 512 bytes to 128 Kbytes is valid.
.Pp
This property can also be referred to by its shortened column name,
.Sy volblock .
.It Sy written
The amount of space
.Sy referenced
by this dataset, that was written since the previous snapshot
.Pq i.e. that is not referenced by the previous snapshot .
.It Sy written Ns @ Ns Ar snapshot
The amount of
.Sy 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.
.Pp
The
.Ar snapshot
may be specified as a short snapshot name
.Pq just the part after the Sy @ ,
in which case it will be interpreted as a snapshot in the same filesystem as
this dataset.
The
.Ar snapshot
may be a full snapshot name
.Pq Ar filesystem Ns @ Ns Ar snapshot ,
which for clones may be a snapshot in the origin's filesystem
.Pq or the origin of the origin's filesystem, etc.
.El
.Pp
The following native properties can be used to change the behavior of a ZFS
dataset.
.Bl -tag -width ""
.It Xo
.Sy aclinherit Ns = Ns Sy discard Ns | Ns Sy noallow Ns | Ns
.Sy restricted Ns | Ns Sy passthrough Ns | Ns Sy passthrough-x
.Xc
Controls how ACEs are inherited when files and directories are created.
.Bl -tag -compact -offset 4n -width "passthrough-x"
.It Sy discard
does not inherit any ACEs.
.It Sy noallow
only inherits inheritable ACEs that specify
.Qq deny
permissions.
.It Sy restricted
default, removes the
.Sy write_acl
and
.Sy write_owner
permissions when the ACE is inherited.
.It Sy passthrough
inherits all inheritable ACEs without any modifications.
.It Sy passthrough-x
same meaning as
.Sy passthrough ,
except that the
.Sy owner@ , group@ , No and Sy everyone@
ACEs inherit the execute permission only if the file creation mode also requests
the execute bit.
.El
.Pp
When the property value is set to
.Sy 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.
.Pp
The
.Sy aclinherit
property does not apply to POSIX ACLs.
.It Xo
.Sy aclmode Ns = Ns Sy discard Ns | Ns Sy groupmask Ns | Ns
.Sy passthrough Ns | Ns Sy restricted Ns
.Xc
Controls how an ACL is modified during chmod(2) and how inherited ACEs
are modified by the file creation mode:
.Bl -tag -compact -offset 4n -width "passthrough"
.It Sy discard
default, deletes all
.Sy ACEs
except for those representing
the mode of the file or directory requested by
.Xr chmod 2 .
.It Sy groupmask
reduces permissions granted in all
.Sy ALLOW
entries found in the
.Sy ACL
such that they are no greater than the group permissions specified by
.Xr chmod 2 .
.It Sy 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.
.It Sy restricted
will cause the
.Xr 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.
.Xr 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
.Xr chmod 2
on a file or directory with a non-trivial ACL when
.Sy aclmode
is set to
.Sy restricted ,
you must first remove all ACL entries which do not represent the current mode.
.El
.It Sy acltype Ns = Ns Sy off Ns | Ns Sy nfsv4 Ns | Ns Sy 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
.Sy off .
.Bl -tag -compact -offset 4n -width "posixacl"
.It Sy off
default on Linux, when a file system has the
.Sy acltype
property set to off then ACLs are disabled.
.It Sy noacl
an alias for
.Sy off
.It Sy nfsv4
default on
.Fx ,
indicates that NFSv4-style ZFS ACLs should be used.
These ACLs can be managed with the
.Xr getfacl 1
and
.Xr setfacl 1 .
The
.Sy nfsv4
ZFS ACL type is not yet supported on Linux.
.It Sy 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.
.It Sy posixacl
an alias for
.Sy posix
.El
.Pp
To obtain the best performance when setting
.Sy posix
users are strongly encouraged to set the
.Sy xattr Ns = Ns Sy sa
property.
This will result in the POSIX ACL being stored more efficiently on disk.
But as a consequence, all new extended attributes will only be
accessible from OpenZFS implementations which support the
.Sy xattr Ns = Ns Sy sa
property.
See the
.Sy xattr
property for more details.
.It Sy atime Ns = Ns Sy on Ns | Ns Sy 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
.Sy on
and
.Sy off
are equivalent to the
.Sy atime
and
.Sy noatime
mount options.
The default value is
.Sy on .
See also
.Sy relatime
below.
.It Sy canmount Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Sy noauto
If this property is set to
.Sy off ,
the file system cannot be mounted, and is ignored by
.Nm zfs Cm mount Fl a .
Setting this property to
.Sy off
is similar to setting the
.Sy mountpoint
property to
.Sy none ,
except that the dataset still has a normal
.Sy mountpoint
property, which can be inherited.
Setting this property to
.Sy off
allows datasets to be used solely as a mechanism to inherit properties.
One example of setting
.Sy canmount Ns = Ns Sy off
is to have two datasets with the same
.Sy mountpoint ,
so that the children of both datasets appear in the same directory, but might
have different inherited characteristics.
.Pp
When set to
.Sy noauto ,
a dataset can only be mounted and unmounted explicitly.
The dataset is not mounted automatically when the dataset is created or
imported, nor is it mounted by the
.Nm zfs Cm mount Fl a
command or unmounted by the
.Nm zfs Cm unmount Fl a
command.
.Pp
This property is not inherited.
.It Xo
.Sy checksum Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Sy fletcher2 Ns | Ns
.Sy fletcher4 Ns | Ns Sy sha256 Ns | Ns Sy noparity Ns | Ns
.Sy sha512 Ns | Ns Sy skein Ns | Ns Sy edonr Ns | Ns Sy blake3
.Xc
Controls the checksum used to verify data integrity.
The default value is
.Sy on ,
which automatically selects an appropriate algorithm
.Po currently,
.Sy fletcher4 ,
but this may change in future releases
.Pc .
The value
.Sy off
disables integrity checking on user data.
The value
.Sy 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
.Em NOT
a recommended practice.
.Pp
The
.Sy sha512 ,
.Sy skein ,
.Sy edonr ,
and
.Sy blake3
checksum algorithms require enabling the appropriate features on the pool.
.Pp
Please see
.Xr zpool-features 7
for more information on these algorithms.
.Pp
Changing this property affects only newly-written data.
.It Xo
.Sy compression Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Sy gzip Ns | Ns
.Sy gzip- Ns Ar N Ns | Ns Sy lz4 Ns | Ns Sy lzjb Ns | Ns Sy zle Ns | Ns Sy zstd Ns | Ns
.Sy zstd- Ns Ar N Ns | Ns Sy zstd-fast Ns | Ns Sy zstd-fast- Ns Ar N
.Xc
Controls the compression algorithm used for this dataset.
.Pp
When set to
.Sy on
(the default), indicates that the current default compression algorithm should
be used.
The default balances compression and decompression speed, with compression ratio
and is expected to work well on a wide variety of workloads.
Unlike all other settings for this property,
.Sy 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
.Sy lzjb
or, if the
.Sy lz4_compress
feature is enabled,
.Sy lz4 .
.Pp
The
.Sy lz4
compression algorithm is a high-performance replacement for the
.Sy lzjb
algorithm.
It features significantly faster compression and decompression, as well as a
moderately higher compression ratio than
.Sy lzjb ,
but can only be used on pools with the
.Sy lz4_compress
feature set to
.Sy enabled .
See
.Xr zpool-features 7
for details on ZFS feature flags and the
.Sy lz4_compress
feature.
.Pp
The
.Sy lzjb
compression algorithm is optimized for performance while providing decent data
compression.
.Pp
The
.Sy gzip
compression algorithm uses the same compression as the
.Xr gzip 1
command.
You can specify the
.Sy gzip
level by using the value
.Sy gzip- Ns Ar N ,
where
.Ar N
is an integer from 1
.Pq fastest
to 9
.Pq best compression ratio .
Currently,
.Sy gzip
is equivalent to
.Sy gzip-6
.Po which is also the default for
.Xr gzip 1
.Pc .
.Pp
The
.Sy zstd
compression algorithm provides both high compression ratios and good
performance.
You can specify the
.Sy zstd
level by using the value
.Sy zstd- Ns Ar N ,
where
.Ar N
is an integer from 1
.Pq fastest
to 19
.Pq best compression ratio .
.Sy zstd
is equivalent to
.Sy zstd-3 .
.Pp
Faster speeds at the cost of the compression ratio can be requested by
setting a negative
.Sy zstd
level.
This is done using
.Sy zstd-fast- Ns Ar N ,
where
.Ar N
is an integer in
.Bq Sy 1 Ns - Ns Sy 10 , 20 , 30 , No … , Sy 100 , 500 , 1000
which maps to a negative
.Sy zstd
level.
The lower the level the faster the compression \(em
.Sy 1000
provides the fastest compression and lowest compression ratio.
.Sy zstd-fast
is equivalent to
.Sy zstd-fast- Ns Ar 1 .
.Pp
The
.Sy zle
compression algorithm compresses runs of zeros.
.Pp
This property can also be referred to by its shortened column name
.Sy compress .
Changing this property affects only newly-written data.
.Pp
When any setting except
.Sy off
is selected, compression will explicitly check for blocks consisting of only
zeroes (the NUL byte).
When a zero-filled block is detected, it is stored as
a hole and not compressed using the indicated compression algorithm.
.Pp
Any block being compressed must be no larger than 7/8 of its original size
after compression, otherwise the compression will not be considered worthwhile
and the block saved uncompressed.
Note that when the logical block is less than
8 times the disk sector size this effectively reduces the necessary compression
ratio; for example, 8 KiB blocks on disks with 4 KiB disk sectors must compress
to 1/2
or less of their original size.
.It Xo
.Sy context Ns = Ns Sy none Ns | Ns
.Ar SELinux-User : Ns Ar SELinux-Role : Ns Ar SELinux-Type : Ns Ar Sensitivity-Level
.Xc
This flag sets the SELinux context for all files in the file system under
a mount point for that file system.
See
.Xr selinux 8
for more information.
.It Xo
.Sy fscontext Ns = Ns Sy none Ns | Ns
.Ar SELinux-User : Ns Ar SELinux-Role : Ns Ar SELinux-Type : Ns Ar Sensitivity-Level
.Xc
This flag sets the SELinux context for the file system file system being
mounted.
See
.Xr selinux 8
for more information.
.It Xo
.Sy defcontext Ns = Ns Sy none Ns | Ns
.Ar SELinux-User : Ns Ar SELinux-Role : Ns Ar SELinux-Type : Ns Ar Sensitivity-Level
.Xc
This flag sets the SELinux default context for unlabeled files.
See
.Xr selinux 8
for more information.
.It Xo
.Sy rootcontext Ns = Ns Sy none Ns | Ns
.Ar SELinux-User : Ns Ar SELinux-Role : Ns Ar SELinux-Type : Ns Ar Sensitivity-Level
.Xc
This flag sets the SELinux context for the root inode of the file system.
See
.Xr selinux 8
for more information.
.It Sy copies Ns = Ns Sy 1 Ns | Ns Sy 2 Ns | Ns Sy 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
.Sy used
property and counting against quotas and reservations.
.Pp
Changing this property only affects newly-written data.
Therefore, set this property at file system creation time by using the
.Fl o Sy copies Ns = Ns Ar N
option.
.Pp
Remember that ZFS will not import a pool with a missing top-level vdev.
Do
.Em NOT
create, for example a two-disk striped pool and set
.Sy copies Ns = Ns Ar 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.
.Pp
Encrypted datasets may not have
.Sy copies Ns = Ns Ar 3
since the implementation stores some encryption metadata where the third copy
would normally be.
.It Sy devices Ns = Ns Sy on Ns | Ns Sy off
Controls whether device nodes can be opened on this file system.
The default value is
.Sy on .
The values
.Sy on
and
.Sy off
are equivalent to the
.Sy dev
and