FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/man/man7/zfsprops.7

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    .Dd July 21, 2022
    .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, 1.5g, 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
   .Sy nodev
  mount options.
  .It Xo
  .Sy dedup Ns = Ns Sy off Ns | Ns Sy on Ns | Ns Sy verify Ns | Ns
  .Sy sha256 Ns Oo , Ns Sy verify Oc Ns | Ns Sy sha512 Ns Oo , Ns Sy verify Oc Ns | Ns Sy skein Ns Oo , Ns Sy verify Oc Ns | Ns
  .Sy edonr , Ns Sy verify Ns | Ns Sy blake3 Ns Oo , Ns Sy verify Oc Ns
  .Xc
  Configures deduplication for a dataset.
  The default value is
  .Sy off .
  The default deduplication checksum is
  .Sy sha256
  (this may change in the future).
  When
  .Sy dedup
  is enabled, the checksum defined here overrides the
  .Sy checksum
  property.
  Setting the value to
  .Sy verify
  has the same effect as the setting
  .Sy sha256 , Ns Sy verify .
  .Pp
  If set to
  .Sy 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
  .Sy verify
  is mandatory for the
  .Sy edonr
  algorithm.
  .Pp
  Unless necessary, deduplication should
  .Em not
  be enabled on a system.
  See the
  .Sx Deduplication
  section of
  .Xr zfsconcepts 7 .
  .It Xo
  .Sy dnodesize Ns = Ns Sy legacy Ns | Ns Sy auto Ns | Ns Sy 1k Ns | Ns
  .Sy 2k Ns | Ns Sy 4k Ns | Ns Sy 8k Ns | Ns Sy 16k
  .Xc
  Specifies a compatibility mode or literal value for the size of dnodes in the
  file system.
  The default value is
  .Sy legacy .
  Setting this property to a value other than
  .Sy legacy No requires the Sy large_dnode No pool feature to be enabled .
  .Pp
  Consider setting
  .Sy dnodesize
  to
  .Sy auto
  if the dataset uses the
  .Sy xattr Ns = Ns Sy sa
  property setting and the workload makes heavy use of extended attributes.
  This
  may be applicable to SELinux-enabled systems, Lustre servers, and Samba
  servers, for example.
  Literal values are supported for cases where the optimal
  size is known in advance and for performance testing.
  .Pp
  Leave
  .Sy dnodesize
  set to
  .Sy legacy
  if you need to receive a send stream of this dataset on a pool that doesn't
  enable the
  .Sy large_dnode
  feature, or if you need to import this pool on a system that doesn't support the
  .Sy large_dnode No feature .
  .Pp
  This property can also be referred to by its shortened column name,
  .Sy dnsize .
  .It Xo
  .Sy encryption Ns = Ns Sy off Ns | Ns Sy on Ns | Ns Sy aes-128-ccm Ns | Ns
  .Sy aes-192-ccm Ns | Ns Sy aes-256-ccm Ns | Ns Sy aes-128-gcm Ns | Ns
  .Sy aes-192-gcm Ns | Ns Sy aes-256-gcm
  .Xc
  Controls the encryption cipher suite (block cipher, key length, and mode) used
  for this dataset.
  Requires the
  .Sy encryption
  feature to be enabled on the pool.
  Requires a
  .Sy keyformat
  to be set at dataset creation time.
  .Pp
  Selecting
  .Sy encryption Ns = Ns Sy on
  when creating a dataset indicates that the default encryption suite will be
  selected, which is currently
  .Sy aes-256-gcm .
  In order to provide consistent data protection, encryption must be specified at
  dataset creation time and it cannot be changed afterwards.
  .Pp
  For more details and caveats about encryption see the
  .Sx Encryption
  section of
  .Xr zfs-load-key 8 .
  .It Sy keyformat Ns = Ns Sy raw Ns | Ns Sy hex Ns | Ns Sy passphrase
  Controls what format the user's encryption key will be provided as.
  This property is only set when the dataset is encrypted.
  .Pp
  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:
  .Dl # Nm dd Sy if=/dev/urandom bs=32 count=1 Sy of= Ns Pa /path/to/output/key
  .Pp
  Passphrases must be between 8 and 512 bytes long and will be processed through
  PBKDF2 before being used (see the
  .Sy pbkdf2iters
  property).
  Even though the encryption suite cannot be changed after dataset creation,
  the keyformat can be with
  .Nm zfs Cm change-key .
  .It Xo
  .Sy keylocation Ns = Ns Sy prompt Ns | Ns Sy file:// Ns Ar /absolute/file/path Ns | Ns Sy https:// Ns Ar address Ns | Ns Sy http:// Ns Ar address
  .Xc
  Controls where the user's encryption key will be loaded from by default for
  commands such as
  .Nm zfs Cm load-key
  and
  .Nm zfs Cm mount Fl l .
  This property is only set for encrypted datasets which are encryption roots.
  If unspecified, the default is
  .Sy prompt .
  .Pp
  Even though the encryption suite cannot be changed after dataset creation, the
  keylocation can be with either
  .Nm zfs Cm set
  or
  .Nm zfs Cm change-key .
  If
  .Sy prompt
  is selected ZFS will ask for the key at the command prompt when it is required
  to access the encrypted data (see
  .Nm zfs Cm load-key
  for details).
  This setting will also allow the key to be passed in via the standard input
  stream,
  but users should be careful not to place keys which should be kept secret on
  the command line.
  If a file URI is selected, the key will be loaded from the
  specified absolute file path.
  If an HTTPS or HTTP URL is selected, it will be GETted using
  .Xr fetch 3 ,
  libcurl, or nothing, depending on compile-time configuration and run-time
  availability.
  The
  .Sy SSL_CA_CERT_FILE
  environment variable can be set to set the location
  of the concatenated certificate store.
  The
  .Sy SSL_CA_CERT_PATH
  environment variable can be set to override the location
  of the directory containing the certificate authority bundle.
  The
  .Sy SSL_CLIENT_CERT_FILE
  and
  .Sy SSL_CLIENT_KEY_FILE
  environment variables can be set to configure the path
  to the client certificate and its key.
  .It Sy pbkdf2iters Ns = Ns Ar iterations
  Controls the number of PBKDF2 iterations that a
  .Sy passphrase
  encryption key should be run through when processing it into an encryption key.
  This property is only defined when encryption is enabled and a keyformat of
  .Sy passphrase
  is selected.
  The goal of PBKDF2 is to significantly increase the
  computational difficulty needed to brute force a user's passphrase.
  This is accomplished by forcing the attacker to run each passphrase through a
  computationally expensive hashing function many times before they arrive at the
  resulting key.
  A user who actually knows the passphrase will only have to pay this cost once.
  As CPUs become better at processing, this number should be
  raised to ensure that a brute force attack is still not possible.
  The current default is
  .Sy 350000
  and the minimum is
  .Sy 100000 .
  This property may be changed with
  .Nm zfs Cm change-key .
  .It Sy exec Ns = Ns Sy on Ns | Ns Sy off
  Controls whether processes can be executed from within this file system.
  The default value is
  .Sy on .
  The values
  .Sy on
  and
  .Sy off
  are equivalent to the
  .Sy exec
  and
  .Sy noexec
  mount options.
  .It Sy filesystem_limit Ns = Ns Ar count Ns | Ns Sy 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
  .Sy filesystem_limit
  to
  .Sy on
  a descendent of a filesystem that already has a
  .Sy filesystem_limit
  does not override the ancestor's
  .Sy filesystem_limit ,
  but rather imposes an additional limit.
  This feature must be enabled to be used
  .Po see
  .Xr zpool-features 7
  .Pc .
  .It Sy special_small_blocks Ns = Ns Ar 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.
  .Pp
  Before setting this property, a special class vdev must be added to the
  pool.
  See
  .Xr zpoolconcepts 7
  for more details on the special allocation class.
  .It Sy mountpoint Ns = Ns Pa path Ns | Ns Sy none Ns | Ns Sy legacy
  Controls the mount point used for this file system.
  See the
  .Sx Mount Points
  section of
  .Xr zfsconcepts 7
  for more information on how this property is used.
  .Pp
  When the
  .Sy 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
  .Sy legacy ,
  then they remain unmounted.
  Otherwise, they are automatically remounted in the new location if the property
  was previously
  .Sy legacy
  or
  .Sy 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.
  .It Sy nbmand Ns = Ns Sy on Ns | Ns Sy off
  Controls whether the file system should be mounted with
  .Sy nbmand
  .Pq Non-blocking mandatory locks .
  This is used for SMB clients.
  Changes to this property only take effect when the file system is umounted and
  remounted.
  Support for these locks is scarce and not described by POSIX.
  .It Sy overlay Ns = Ns Sy on Ns | Ns Sy off
  Allow mounting on a busy directory or a directory which already contains
  files or directories.
  This is the default mount behavior for Linux and
  .Fx
  file systems.
  On these platforms the property is
  .Sy on
  by default.
  Set to
  .Sy off
  to disable overlay mounts for consistency with OpenZFS on other platforms.
  .It Sy primarycache Ns = Ns Sy all Ns | Ns Sy none Ns | Ns Sy metadata
  Controls what is cached in the primary cache
  .Pq ARC .
  If this property is set to
  .Sy all ,
  then both user data and metadata is cached.
  If this property is set to
  .Sy none ,
  then neither user data nor metadata is cached.
  If this property is set to
  .Sy metadata ,
  then only metadata is cached.
  The default value is
  .Sy all .
  .It Sy quota Ns = Ns Ar size Ns | Ns Sy 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.
  .Pp
  Quotas cannot be set on volumes, as the
  .Sy volsize
  property acts as an implicit quota.
  .It Sy snapshot_limit Ns = Ns Ar count Ns | Ns Sy none
  Limits the number of snapshots that can be created on a dataset and its
  descendents.
  Setting a
  .Sy snapshot_limit
  on a descendent of a dataset that already has a
  .Sy snapshot_limit
  does not override the ancestor's
  .Sy 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
  .Po see
  .Xr zpool-features 7
  .Pc .
  .It Sy userquota@ Ns Ar user Ns = Ns Ar size Ns | Ns Sy none
  Limits the amount of space consumed by the specified user.
  User space consumption is identified by the
  .Sy userspace@ Ns Ar user
  property.
  .Pp
  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
  .Er EDQUOT
  error message.
  See the
  .Nm zfs Cm userspace
  command 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 userquota
  privilege with
  .Nm zfs Cm allow ,
  can get and set everyone's quota.
  .Pp
  This property is not available on volumes, on file systems before version 4, or
  on pools before version 15.
  The
  .Sy userquota@ 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 userobjquota@ Ns Ar user Ns = Ns Ar size Ns | Ns Sy none
  The
  .Sy userobjquota
  is similar to
  .Sy userquota
  but it limits the number of objects a user can create.
  Please refer to
  .Sy userobjused
  for more information about how objects are counted.
  .It Sy groupquota@ Ns Ar group Ns = Ns Ar size Ns | Ns Sy none
  Limits the amount of space consumed by the specified group.
  Group space consumption is identified by the
  .Sy groupused@ Ns Ar group
  property.
  .Pp
  Unprivileged users can access only their own groups' space usage.
  The root user, or a user who has been granted the
  .Sy groupquota
  privilege with
  .Nm zfs Cm allow ,
  can get and set all groups' quotas.
  .It Sy groupobjquota@ Ns Ar group Ns = Ns Ar size Ns | Ns Sy none
  The
  .Sy groupobjquota
  is similar to
  .Sy groupquota
  but it limits number of objects a group can consume.
  Please refer to
  .Sy userobjused
  for more information about how objects are counted.
  .It Sy projectquota@ Ns Ar project Ns = Ns Ar size Ns | Ns Sy none
  Limits the amount of space consumed by the specified project.
  Project space consumption is identified by the
  .Sy projectused@ Ns Ar project
  property.
  Please refer to
  .Sy projectused
  for more information about how project is identified and set/changed.
  .Pp
  The root user, or a user who has been granted the
  .Sy projectquota
  privilege with
  .Nm zfs allow ,
  can access all projects' quota.
  .It Sy projectobjquota@ Ns Ar project Ns = Ns Ar size Ns | Ns Sy none
  The
  .Sy projectobjquota
  is similar to
  .Sy projectquota
  but it limits number of objects a project can consume.
  Please refer to
  .Sy userobjused
  for more information about how objects are counted.
  .It Sy readonly Ns = Ns Sy on Ns | Ns Sy off
  Controls whether this dataset can be modified.
  The default value is
  .Sy off .
  The values
  .Sy on
  and
  .Sy off
  are equivalent to the
  .Sy ro
  and
  .Sy rw
  mount options.
  .Pp
  This property can also be referred to by its shortened column name,
  .Sy rdonly .
  .It Sy recordsize Ns = Ns Ar size
  Specifies a suggested block size for files in the file system.
  This property is designed solely for use with database workloads that access
  files in fixed-size records.
  ZFS automatically tunes block sizes according to internal algorithms optimized
  for typical access patterns.
  .Pp
  For databases that create very large files but access them in small random
  chunks, these algorithms may be suboptimal.
  Specifying a
  .Sy recordsize
  greater than or equal to the record size of the database can result in
  significant performance gains.
  Use of this property for general purpose file systems is strongly discouraged,
  and may adversely affect performance.
  .Pp
  The size specified must be a power of two greater than or equal to
  .Ar 512 B
  and less than or equal to
  .Ar 128 KiB .
  If the
  .Sy large_blocks
  feature is enabled on the pool, the size may be up to
  .Ar 1 MiB .
  See
  .Xr zpool-features 7
  for details on ZFS feature flags.
  .Pp
  Changing the file system's
  .Sy recordsize
  affects only files created afterward; existing files are unaffected.
  .Pp
  This property can also be referred to by its shortened column name,
  .Sy recsize .
  .It Sy redundant_metadata Ns = Ns Sy all Ns | Ns Sy most Ns | Ns Sy some Ns | Ns Sy 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 addition to any redundancy provided at the pool level
  .Pq e.g. by mirroring or RAID-Z ,
  and is in addition to an extra copy specified by the
  .Sy copies
  property
  .Pq up to a total of 3 copies .
  For example if the pool is mirrored,
  .Sy copies Ns = Ns 2 ,
  and
  .Sy redundant_metadata Ns = Ns Sy most ,
  then ZFS stores 6 copies of most metadata, and 4 copies of data and some
  metadata.
  .Pp
  When set to
  .Sy 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
  .Po which is
  .Sy recordsize
  bytes long
  .Pc
  can be lost.
  .Pp
  When set to
  .Sy 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
  .Po of
  .Sy recordsize
  bytes each
  .Pc
  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.
  .Pp
  When set to
  .Sy 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.
  .Pp
  When set to
  .Sy none ,
  ZFS does not store any copies of metadata redundantly.
  If a single on-disk block is corrupt, an entire dataset can be lost.
  .Pp
  The default value is
  .Sy all .
  .It Sy refquota Ns = Ns Ar size Ns | Ns Sy none
  Limits the amount of space a dataset can consume.
  This property enforces a hard limit on the amount of space used.
  This hard limit does not include space used by descendents, including file
  systems and snapshots.
  .It Sy refreservation Ns = Ns Ar size Ns | Ns Sy none Ns | Ns Sy 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
  .Sy refreservation .
  The
  .Sy refreservation
  reservation is accounted for in the parent datasets' space used, and counts
  against the parent datasets' quotas and reservations.
  .Pp
  If
  .Sy 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
  .Qq referenced
  bytes in the dataset.
  .Pp
  If
  .Sy refreservation
  is set to
  .Sy auto ,
  a volume is thick provisioned
  .Po or
  .Qq not sparse
  .Pc .
  .Sy refreservation Ns = Ns Sy auto
  is only supported on volumes.
  See
  .Sy volsize
  in the
  .Sx Native Properties
  section for more information about sparse volumes.
  .Pp
  This property can also be referred to by its shortened column name,
  .Sy refreserv .
  .It Sy relatime Ns = Ns Sy on Ns | Ns Sy off
  Controls the manner in which the access time is updated when
  .Sy atime Ns = Ns Sy 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
  .Sy on .
  The values
  .Sy on
  and
  .Sy off
  are equivalent to the
  .Sy relatime
  and
  .Sy norelatime
  mount options.
  .It Sy reservation Ns = Ns Ar size Ns | Ns Sy none
  The minimum amount of space guaranteed to a dataset and its descendants.
  When the amount of space used is below this value, the dataset is treated as if
  it were taking up the amount of space specified by its reservation.
  Reservations are accounted for in the parent datasets' space used, and count
  against the parent datasets' quotas and reservations.
  .Pp
  This property can also be referred to by its shortened column name,
  .Sy reserv .
  .It Sy secondarycache Ns = Ns Sy all Ns | Ns Sy none Ns | Ns Sy metadata
  Controls what is cached in the secondary cache
  .Pq L2ARC .
  If this property is set to
  .Sy all ,
  then both user data and metadata is cached.
  If this property is set to
  .Sy none ,
  then neither user data nor metadata is cached.
  If this property is set to
  .Sy metadata ,
  then only metadata is cached.
  The default value is
  .Sy all .
  .It Sy setuid Ns = Ns Sy on Ns | Ns Sy off
  Controls whether the setuid bit is respected for the file system.
  The default value is
  .Sy on .
  The values
  .Sy on
  and
  .Sy off
  are equivalent to the
  .Sy suid
  and
  .Sy nosuid
  mount options.
  .It Sy sharesmb Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Ar opts
  Controls whether the file system is shared by using
  .Sy Samba USERSHARES
  and what options are to be used.
  Otherwise, the file system is automatically shared and unshared with the
  .Nm zfs Cm share
  and
  .Nm zfs Cm unshare
  commands.
  If the property is set to on, the
  .Xr net 8
  command is invoked to create a
  .Sy USERSHARE .
  .Pp
  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.
  .Pp
  If the
  .Sy sharesmb
  property is set to
  .Sy off ,
  the file systems are unshared.
  .Pp
  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 \(em
  .Xr passwd 5 Ns / Ns Xr shadow 5 Ns - ,
  LDAP- or
  .Xr smbpasswd 5 Ns -based )
  by default.
  This means that any additional access control
  (disallow specific user specific access etc) must be done on the underlying file
  system.
  .It Sy sharenfs Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Ar opts
  Controls whether the file system is shared via NFS, and what options are to be
  used.
  A file system with a
  .Sy sharenfs
  property of
  .Sy off
  is managed with the
  .Xr exportfs 8
  command and entries in the
  .Pa /etc/exports
  file.
  Otherwise, the file system is automatically shared and unshared with the
  .Nm zfs Cm share
  and
  .Nm zfs Cm unshare
  commands.
  If the property is set to
  .Sy on ,
  the dataset is shared using the default options:
  .Dl sec=sys,rw,crossmnt,no_subtree_check
  .Pp
  Please note that the options are comma-separated, unlike those found in
  .Xr exports 5 .
  This is done to negate the need for quoting, as well as to make parsing
  with scripts easier.
  .Pp
  See
  .Xr exports 5
  for the meaning of the default options.
  Otherwise, the
  .Xr exportfs 8
  command is invoked with options equivalent to the contents of this property.
  .Pp
  When the
  .Sy sharenfs
  property is changed for a dataset, the dataset and any children inheriting the
  property are re-shared with the new options, only if the property was previously
  .Sy off ,
  or if they were shared before the property was changed.
  If the new property is
  .Sy off ,
  the file systems are unshared.
  .It Sy logbias Ns = Ns Sy latency Ns | Ns Sy throughput
  Provide a hint to ZFS about handling of synchronous requests in this dataset.
  If
  .Sy logbias
  is set to
  .Sy latency
  .Pq the default ,
  ZFS will use pool log devices
  .Pq if configured
  to handle the requests at low latency.
  If
  .Sy logbias
  is set to
  .Sy throughput ,
  ZFS will not use configured pool log devices.
  ZFS will instead optimize synchronous operations for global pool throughput and
  efficient use of resources.
  .It Sy snapdev Ns = Ns Sy hidden Ns | Ns Sy visible
  Controls whether the volume snapshot devices under
  .Pa /dev/zvol/ Ns Aq Ar pool
  are hidden or visible.
  The default value is
  .Sy hidden .
  .It Sy snapdir Ns = Ns Sy hidden Ns | Ns Sy visible
  Controls whether the
  .Pa .zfs
  directory is hidden or visible in the root of the file system as discussed in
  the
  .Sx Snapshots
  section of
  .Xr zfsconcepts 7 .
  The default value is
  .Sy hidden .
  .It Sy sync Ns = Ns Sy standard Ns | Ns Sy always Ns | Ns Sy disabled
  Controls the behavior of synchronous requests
  .Pq e.g. fsync, O_DSYNC .
  .Sy 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
  .Pq this is the default .
  .Sy always
  causes every file system transaction to be written and flushed before its
  system call returns.
  This has a large performance penalty.
  .Sy 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.
  .It Sy version Ns = Ns Ar N Ns | Ns Sy current
  The on-disk version of this file system, which is independent of the pool
  version.
  This property can only be set to later supported versions.
  See the
  .Nm zfs Cm upgrade
  command.
  .It Sy volsize Ns = Ns Ar 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
  .Sy refreservation
  is set instead.
  Any changes to
  .Sy volsize
  are reflected in an equivalent change to the reservation
  .Pq or Sy refreservation .
  The
  .Sy volsize
  can only be set to a multiple of
  .Sy volblocksize ,
  and cannot be zero.
  .Pp
  The reservation is kept equal to the volume's logical size to prevent unexpected
  behavior for consumers.
  Without the reservation, the volume could run out of space, resulting in
  undefined behavior or data corruption, depending on how the volume is used.
  These effects can also occur when the volume size is changed while it is in use
  .Pq particularly when shrinking the size .
  Extreme care should be used when adjusting the volume size.
  .Pp
  Though not recommended, a
  .Qq sparse volume
  .Po also known as
  .Qq thin provisioned
  .Pc
  can be created by specifying the
  .Fl s
  option to the
  .Nm zfs Cm create Fl V
  command, or by changing the value of the
  .Sy refreservation
  property
  .Po or
  .Sy reservation
  property on pool version 8 or earlier
  .Pc
  after the volume has been created.
  A
  .Qq sparse volume
  is a volume where the value of
  .Sy 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
  .Er ENOSPC
  when the pool is low on space.
  For a sparse volume, changes to
  .Sy volsize
  are not reflected in the
  .Sy refreservation .
  A volume that is not sparse is said to be
  .Qq thick provisioned .
  A sparse volume can become thick provisioned by setting
  .Sy refreservation
  to
  .Sy auto .
  .It Sy volmode Ns = Ns Sy default Ns | Ns Sy full Ns | Ns Sy geom Ns | Ns Sy dev Ns | Ns Sy none
  This property specifies how volumes should be exposed to the OS.
  Setting it to
  .Sy full
  exposes volumes as fully fledged block devices, providing maximal
  functionality.
  The value
  .Sy geom
  is just an alias for
  .Sy full
  and is kept for compatibility.
  Setting it to
  .Sy dev
  hides its partitions.
  Volumes with property set to
  .Sy none
  are not exposed outside ZFS, but can be snapshotted, cloned, replicated, etc,
  that can be suitable for backup purposes.
  Value
  .Sy default
  means that volumes exposition is controlled by system-wide tunable
  .Sy zvol_volmode ,
  where
  .Sy full ,
  .Sy dev
  and
  .Sy none
  are encoded as 1, 2 and 3 respectively.
  The default value is
  .Sy full .
  .It Sy vscan Ns = Ns Sy on Ns | Ns Sy 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
  .Sy off .
  This property is not used by OpenZFS.
  .It Sy xattr Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Sy 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.
  .Pp
  The default value of
  .Sy 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
  .Xr getxattr 2
  and
  .Xr setxattr 2
  system calls limit the maximum size to
  .Sy 64K .
  This is the most compatible
  style of extended attribute and is supported by all ZFS implementations.
  .Pp
  System-attribute-based xattrs can be enabled by setting the value to
  .Sy sa .
  The key advantage of this type of xattr is improved performance.
  Storing extended attributes as system attributes
  significantly decreases the amount of disk I/O required.
  Up to
  .Sy 64K
  of data may be stored per-file in the space reserved for system attributes.
  If there is not enough space available for an extended attribute
  then it will be automatically written as a directory-based xattr.
  System-attribute-based extended attributes are not accessible
  on platforms which do not support the
  .Sy xattr Ns = Ns Sy sa
  feature.
  OpenZFS supports
  .Sy xattr Ns = Ns Sy sa
  on both
  .Fx
  and Linux.
  .Pp
  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.
  .Pp
  The values
  .Sy on
  and
  .Sy off
  are equivalent to the
  .Sy xattr
  and
  .Sy noxattr
  mount options.
  .It Sy jailed Ns = Ns Sy off Ns | Ns Sy on
  Controls whether the dataset is managed from a jail.
  See
  .Xr zfs-jail 8
  for more information.
  Jails are a
  .Fx
  feature and are not relevant on other platforms.
  The default value is
  .Sy off .
  .It Sy zoned Ns = Ns Sy on Ns | Ns Sy off
  Controls whether the dataset is managed from a non-global zone or namespace.
  The default value is
  .Sy off .
  .El
  .Pp
  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
  .Nm zfs Cm create
  or
  .Nm zpool Cm create
  commands, these properties are inherited from the parent dataset.
  If the parent dataset lacks these properties due to having been created prior to
  these features being supported, the new file system will have the default values
  for these properties.
  .Bl -tag -width ""
  .It Xo
  .Sy casesensitivity Ns = Ns Sy sensitive Ns | Ns
  .Sy insensitive Ns | Ns Sy mixed
  .Xc
  Indicates whether the file name matching algorithm used by the file system
  should be case-sensitive, case-insensitive, or allow a combination of both
  styles of matching.
  The default value for the
  .Sy casesensitivity
  property is
  .Sy sensitive .
  Traditionally,
  .Ux
  and POSIX file systems have case-sensitive file names.
  .Pp
  The
  .Sy mixed
  value for the
  .Sy casesensitivity
  property indicates that the file system can support requests for both
  case-sensitive and case-insensitive matching behavior.
  Currently, case-insensitive matching behavior on a file system that supports
  mixed behavior is limited to the SMB server product.
  For more information about the
  .Sy mixed
  value behavior, see the "ZFS Administration Guide".
  .It Xo
  .Sy normalization Ns = Ns Sy none Ns | Ns Sy formC Ns | Ns
  .Sy formD Ns | Ns Sy formKC Ns | Ns Sy formKD
  .Xc
  Indicates whether the file system should perform a
  .Sy unicode
  normalization of file names whenever two file names are compared, and which
  normalization algorithm should be used.
  File names are always stored unmodified, names are normalized as part of any
  comparison process.
  If this property is set to a legal value other than
  .Sy none ,
  and the
  .Sy utf8only
  property was left unspecified, the
  .Sy utf8only
  property is automatically set to
  .Sy on .
  The default value of the
  .Sy normalization
  property is
  .Sy none .
  This property cannot be changed after the file system is created.
  .It Sy utf8only Ns = Ns Sy on Ns | Ns Sy off
  Indicates whether the file system should reject file names that include
  characters that are not present in the
  .Sy UTF-8
  character code set.
  If this property is explicitly set to
  .Sy off ,
  the normalization property must either not be explicitly set or be set to
  .Sy none .
  The default value for the
  .Sy utf8only
  property is
  .Sy off .
  This property cannot be changed after the file system is created.
  .El
  .Pp
  The
  .Sy casesensitivity ,
  .Sy normalization ,
  and
  .Sy utf8only
  properties are also new permissions that can be assigned to non-privileged users
  by using the ZFS delegated administration feature.
  .
  .Ss Temporary Mount Point Properties
  When a file system is mounted, either through
  .Xr mount 8
  for legacy mounts or the
  .Nm zfs Cm 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:
  .Bl -tag -compact -offset Ds -width "rootcontext="
  .It Sy atime
  atime/noatime
  .It Sy canmount
  auto/noauto
  .It Sy devices
  dev/nodev
  .It Sy exec
  exec/noexec
  .It Sy readonly
  ro/rw
  .It Sy relatime
  relatime/norelatime
  .It Sy setuid
  suid/nosuid
  .It Sy xattr
  xattr/noxattr
  .It Sy nbmand
  mand/nomand
  .It Sy context Ns =
  context=
  .It Sy fscontext Ns =
  fscontext=
  .It Sy defcontext Ns =
  defcontext=
  .It Sy rootcontext Ns =
  rootcontext=
  .El
  .Pp
  In addition, these options can be set on a per-mount basis using the
  .Fl 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
  .Sy nosuid
  option is an alias for
  .Sy nodevices , Ns Sy nosetuid .
  These properties are reported as
  .Qq temporary
  by the
  .Nm zfs Cm get
  command.
  If the properties are changed while the dataset is mounted, the new setting
  overrides any temporary settings.
  .
  .Ss 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
  .Pq file systems, volumes, and snapshots .
  .Pp
  User property names must contain a colon
  .Pq Qq Sy \&:
  character to distinguish them from native properties.
  They may contain lowercase letters, numbers, and the following punctuation
  characters: colon
  .Pq Qq Sy \&: ,
  dash
  .Pq Qq Sy - ,
  period
  .Pq Qq Sy \&. ,
  and underscore
  .Pq Qq Sy _ .
  The expected convention is that the property name is divided into two portions
  such as
  .Ar module : Ns Ar property ,
  but this namespace is not enforced by ZFS.
  User property names can be at most 256 characters, and cannot begin with a dash
  .Pq Qq Sy - .
  .Pp
  When making programmatic use of user properties, it is strongly suggested to use
  a reversed DNS domain name for the
  .Ar module
  component of property names to reduce the chance that two
  independently-developed packages use the same property name for different
  purposes.
  .Pp
  The values of user properties are arbitrary strings, are always inherited, and
  are never validated.
  All of the commands that operate on properties
  .Po Nm zfs Cm list ,
  .Nm zfs Cm get ,
  .Nm zfs Cm set ,
  and so forth
  .Pc
  can be used to manipulate both native properties and user properties.
  Use the
  .Nm zfs Cm 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.

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