Reorganize zfs(8) man page into sections

Most subcommands got their own manpages (e.g. create). Some related
commands grouped into a single manpage and symlinks created (e.g. set, 
get, and inherit). I did this when topics were either too short to 
warrant their own file or so interrelated that a user would want to
refer between commands in the same file.

Corrected .Sx internal references to .Xr cross refs; lots of .Sx 
references from when text was all in zfs.8 needed to be changed to 
.Xr zfs-$SUBCOMMAND 8 cross references.

Divided subcommand list in zfs(8) into sections of related 
functionality. This required writing new descriptions for some 
commands.

Preserved ".Os Linux", `.Os` macro parsing behavior differs between 
mandoc from the "BSD" mandoc package (available on Ubuntu) and man 
from Ubuntu's man-db package, which calls groff to format the manpages.

Groff handles the `.Os` macro differently and wrongly, defaulting 
it to "BSD" in `/usr/share/groff/*/tmac/mdoc/doc-common`, instead of
getting the default from `uname`.

A future set of changes will introduce build-time preprocessing of
manpages for platform-specific documentation and can insert the
correct operating system name.

Added SEE ALSO sections, the newly-divided zfs-*.8 subcommand man
pages needed their own SEE ALSO sections pointing to related
subcommands and, in some cases, documentation from other packages
(e.g. zfs-share.8).

Reviewed-by: Matt Ahrens <[email protected]>
Reviewed-by: Kjeld Schouten <[email protected]>
Reviewed-by: Sean Eric Fagan <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Ross Williams <[email protected]>
Closes #9559 

1 files changed, 1884 insertions, 0 deletions

diff --git a/man/man8/zfsprops.8 b/man/man8/zfsprops.8
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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
+.\" or http://www.opensolaris.org/os/licensing.
+.\" See the License for the specific language governing permissions
+.\" and limitations under the License.
+.\"
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+.\" If applicable, add the following below this CDDL HEADER, with the
+.\" fields enclosed by brackets "[]" replaced with your own identifying
+.\" information: Portions Copyright [yyyy] [name of copyright owner]
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+.\" CDDL HEADER END
+.\"
+.\"
+.\" Copyright (c) 2009 Sun Microsystems, Inc. All Rights Reserved.
+.\" Copyright 2011 Joshua M. Clulow <[email protected]>
+.\" Copyright (c) 2011, 2019 by Delphix. All rights reserved.
+.\" 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 2019 Richard Laager. All rights reserved.
+.\" Copyright 2018 Nexenta Systems, Inc.
+.\" Copyright 2019 Joyent, Inc.
+.\"
+.Dd June 30, 2019
+.Dt ZFSPROPS 8
+.Os Linux
+.Sh NAME
+.Nm zfsprops
+.Nd Native properties and user-defined 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
+.Em 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
+, 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
+.Sy zfs receive -s ,
+this opaque token can be provided to
+.Sy zfs send -t
+to resume and complete the
+.Sy zfs 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 ,
+or
+.Sy snapshot .
+.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
+.Em Snapshots
+section of
+.Xr zfsconcepts 8
+.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
+.Dv 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 Em 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
+and
+.Nm ls Fl s .
+See the
+.Nm zfs Cm userspace
+subcommand 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 Em ...
+properties are not displayed by
+.Nm zfs Cm get Sy all .
+The user's name must be appended after the @ symbol, using one of the following
+forms:
+.Bl -bullet -width ""
+.It
+.Em POSIX name
+.Po for example,
+.Sy joe
+.Pc
+.It
+.Em POSIX numeric ID
+.Po for example,
+.Sy 789
+.Pc
+.It
+.Em SID name
+.Po for example,
+.Sy joe.smith@mydomain
+.Pc
+.It
+.Em SID numeric ID
+.Po for example,
+.Sy S-1-123-456-789
+.Pc
+.El
+.Pp
+Files created on Linux always have POSIX owners.
+.It Sy userobjused Ns @ Ns Em 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=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=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 Em 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 Em 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 Em 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 Em 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 Em 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 Em 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 Em 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=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=sa
+no additional internal objects are required. See the
+.Sy userobjused Ns @ Ns Em 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 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 8 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 Em 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
+.Em snapshot
+may be specified as a short snapshot name
+.Po just the part after the
+.Sy @
+.Pc ,
+in which case it will be interpreted as a snapshot in the same filesystem as
+this dataset.
+The
+.Em snapshot
+may be a full snapshot name
+.Po Em filesystem Ns @ Ns Em snapshot Pc ,
+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 -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@ ,
+.Sy group@ ,
+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 Sy acltype Ns = Ns Sy off Ns | Ns Sy noacl Ns | Ns Sy posixacl
+Controls whether ACLs are enabled and if so what type of ACL to use.
+.Bl -tag -width "posixacl"
+.It Sy off
+default, 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 posixacl
+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.
+.El
+.Pp
+To obtain the best performance when setting
+.Sy posixacl
+users are strongly encouraged to set the
+.Sy xattr=sa
+property. This will result in the POSIX ACL being stored more efficiently on
+disk. But as a consequence, all new extended attributes will only be
+accessible from OpenZFS implementations which support the
+.Sy xattr=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
+.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
+.Sy NOT
+a recommended practice.
+.Pp
+The
+.Sy sha512 ,
+.Sy skein ,
+and
+.Sy edonr
+checksum algorithms require enabling the appropriate features on the pool.
+These pool features are not supported by GRUB and must not be used on the
+pool if GRUB needs to access the pool (e.g. for /boot).
+.Pp
+Please see
+.Xr zpool-features 5
+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 Em N Ns | Ns Sy lz4 Ns | Ns Sy lzjb Ns | Ns Sy zle
+.Xc
+Controls the compression algorithm used for this dataset.
+.Pp
+Setting compression to
+.Sy on
+indicates that the current default compression algorithm should be used.
+The default balances compression and decompression speed, with compression ratio
+and is expected to work well on a wide variety of workloads.
+Unlike all other settings for this property,
+.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 5
+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 Em N ,
+where
+.Em 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 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 8k blocks on disks with 4k disk sectors must compress to 1/2
+or less of their original size.
+.It Xo
+.Sy context Ns = Ns Sy none Ns | Ns
+.Em SELinux_User:SElinux_Role:Selinux_Type: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
+.Em SELinux_User:SElinux_Role:Selinux_Type: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
+.Em SELinux_User:SElinux_Role:Selinux_Type: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
+.Em SELinux_User:SElinux_Role:Selinux_Type: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
+.Sy NOT
+create, for example a two-disk striped pool and set
+.Sy copies=2
+on some datasets thinking you have setup redundancy for them. When a disk
+fails you will not be able to import the pool and will have lost all of your
+data.
+.Pp
+Encrypted datasets may not have
+.Sy copies Ns = Ns Em 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[,verify] Ns | Ns Sy sha512[,verify] Ns | Ns Sy skein[,verify] Ns | Ns
+.Sy edonr,verify
+.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,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 NOT be enabled on a system. See the
+.Em Deduplication
+section of
+.Xr zfsconcepts 8 .
+.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
+requires the large_dnode pool feature to be enabled.
+.Pp
+Consider setting
+.Sy dnodesize
+to
+.Sy auto
+if the dataset uses the
+.Sy xattr=sa
+property setting and the workload makes heavy use of extended attributes. This
+may be applicable to SELinux-enabled systems, Lustre servers, and Samba
+servers, for example. Literal values are supported for cases where the optimal
+size is known in advance and for performance testing.
+.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 large_dnode feature, or if you need to import this pool on a system
+that doesn't support the large_dnode 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-ccm .
+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
+.Sy Encryption
+section.
+.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:
+.Bd -literal
+# dd if=/dev/urandom of=/path/to/output/key bs=32 count=1
+.Ed
+.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 Em </absolute/file/path>
+.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 Cm -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 STDIN,
+but users should be careful not to place keys which should be kept secret on
+the command line. If a file URI is selected, the key will be loaded from the
+specified absolute file path.
+.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 Em 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 5
+.Pc .
+.It Sy special_small_blocks Ns = Ns Em size
+This value represents the threshold block size for including small file
+blocks into the special allocation class. Blocks smaller than or equal to this
+value will be assigned to the special allocation class while greater blocks
+will be assigned to the regular class. Valid values are zero or a power of two
+from 512B up to 128K. 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 zpool 8
+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
+.Em Mount Points
+section of
+.Xr zfsconcepts 8
+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.
+See
+.Xr mount 8
+for more information on
+.Sy nbmand
+mounts. This property is not used on Linux.
+.It Sy overlay Ns = Ns Sy off Ns | Ns Sy on
+Allow mounting on a busy directory or a directory which already contains
+files or directories. This is the default mount behavior for Linux file systems.
+For consistency with OpenZFS on other platforms overlay mounts are
+.Sy off
+by default. Set to
+.Sy on
+to enable overlay mounts.
+.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 Em 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 Em 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 5
+.Pc .
+.It Sy userquota@ Ns Em user Ns = Ns Em 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 Em 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
+subcommand 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 Em ...
+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
+.It
+.Em POSIX name
+.Po for example,
+.Sy joe
+.Pc
+.It
+.Em POSIX numeric ID
+.Po for example,
+.Sy 789
+.Pc
+.It
+.Em SID name
+.Po for example,
+.Sy joe.smith@mydomain
+.Pc
+.It
+.Em SID numeric ID
+.Po for example,
+.Sy S-1-123-456-789
+.Pc
+.El
+.Pp
+Files created on Linux always have POSIX owners.
+.It Sy userobjquota@ Ns Em user Ns = Ns Em 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 Em group Ns = Ns Em 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 Em 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 Em group Ns = Ns Em 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 Em project Ns = Ns Em 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 Em 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 Em project Ns = Ns Em 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 Em 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 512 and less
+than or equal to 128 Kbytes.
+If the
+.Sy large_blocks
+feature is enabled on the pool, the size may be up to 1 Mbyte.
+See
+.Xr zpool-features 5
+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
+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 100 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
+The default value is
+.Sy all .
+.It Sy refquota Ns = Ns Em 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 Em 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=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 off .
+The values
+.Sy on
+and
+.Sy off
+are equivalent to the
+.Sy relatime
+and
+.Sy norelatime
+mount options.
+.It Sy reservation Ns = Ns Em 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 Em 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", ie. read and write permissions) and no guest
+access (which means Samba must be able to authenticate a real user, system
+passwd/shadow, LDAP or smbpasswd based) by default. This means that any
+additional access control (disallow specific user specific access etc) must
+be done on the underlying file system.
+.It Sy sharenfs Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Em 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
+.Em /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:
+.Pp
+.Em sec=sys,rw,crossmnt,no_subtree_check
+.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
+.Em /dev/zvol/<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
+.Em Snapshots
+section of
+.Xr zfsconcepts 8 .
+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
+.Tn 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 Em 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 Em 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
+.Po or
+.Sy refreservation
+.Pc .
+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 Cm default | full | geom | dev | 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
+.Va zvol_volmode ,
+where
+.Sy full ,
+.Sy dev
+and
+.Sy none
+are encoded as 1, 2 and 3 respectively.
+The default values 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 on Linux.
+.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 64K. This is the most compatible
+style of extended attribute and is supported by all OpenZFS 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 IO required. Up to 64K of data may be stored per-file in the space
+reserved for system attributes. If there is not enough space available for
+an extended attribute then it will be automatically written as a directory
+based xattr. System attribute based extended attributes are not accessible
+on platforms which do not support the
+.Sy xattr=sa
+feature.
+.Pp
+The use of system attribute based xattrs is strongly encouraged for users of
+SELinux or POSIX ACLs. Both of these features heavily rely of 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 zoned Ns = Ns Sy on Ns | Ns Sy off
+Controls whether the dataset is managed from a non-global zone. Zones are a
+Solaris feature and are not relevant on Linux. 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
+.Tn 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:
+.Bd -literal
+    PROPERTY                MOUNT OPTION
+    atime                   atime/noatime
+    canmount                auto/noauto
+    devices                 dev/nodev
+    exec                    exec/noexec
+    readonly                ro/rw
+    relatime                relatime/norelatime
+    setuid                  suid/nosuid
+    xattr                   xattr/noxattr
+.Ed
+.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 \&, 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
+.Em module Ns \&: Ns Em 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
+.Sy DNS
+domain name for the
+.Em 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.