DESCRIPTION
The
zfs command configures ZFS datasets within a ZFS storage pool, as described in
zpool(1M). A dataset is identified by a unique path within the ZFS namespace. For example:
pool/{filesystem,volume,snapshot}
where the maximum length of a dataset name is
MAXNAMELEN (256 bytes).
A dataset can be one of the following:
-
file system
-
A ZFS dataset of type filesystem can be mounted within the standard system namespace and behaves like other file systems. While ZFS file systems are designed to be POSIX compliant, known issues exist that prevent compliance in some cases. Applications that depend on standards conformance might fail due to non-standard behavior when checking file system free space.
-
volume
-
A logical volume exported as a raw or block device. This type of dataset should only be used under special circumstances. File systems are typically used in most environments.
-
snapshot
-
A read-only version of a file system or volume at a given point in time. It is specified as filesystem@name or volume@name.
ZFS File System Hierarchy
A ZFS storage pool is a logical collection of devices that provide space for datasets. A storage pool is also the root of the ZFS file system hierarchy.
The root of the pool can be accessed as a file system, such as mounting and unmounting, taking snapshots, and setting properties. The physical storage characteristics, however, are managed by the
zpool(1M) command.
See
zpool(1M) for more information on creating and administering pools.
Snapshots
A snapshot is a read-only copy of a file system or volume. Snapshots can be created extremely quickly, and initially consume no additional space within the pool. As data within the active dataset changes, the snapshot consumes more data than would otherwise be shared with the active dataset.
Snapshots can have arbitrary names. Snapshots of volumes can be cloned or rolled back, but cannot be accessed independently.
File system snapshots can be accessed under the
.zfs/snapshot directory in the root of the file system. Snapshots are automatically mounted on demand and may be unmounted at regular intervals. The visibility of the
.zfs directory can be controlled by the snapdir property.
Clones
A clone is a writable volume or file system whose initial contents are the same as another dataset. As with snapshots, creating a clone is nearly instantaneous, and initially consumes no additional space.
Clones can only be created from a snapshot. When a snapshot is cloned, it creates an implicit dependency between the parent and child. Even though the clone is created somewhere else in the dataset hierarchy, the original snapshot cannot be destroyed as long as a clone exists. The
origin property exposes this dependency, and the
destroy command lists any such dependencies, if they exist.
The clone parent-child dependency relationship can be reversed by using the
promote subcommand. This causes the “origin” file system to become a clone of the specified file system, which makes it possible to destroy the file system that the clone was created from.
Mount Points
Creating a ZFS file system is a simple operation, so the number of file systems per system is likely to be numerous. To cope with this, ZFS automatically manages mounting and unmounting file systems without the need to edit the
/etc/vfstab file. All automatically managed file systems are mounted by ZFS at boot time.
By default, file systems are mounted under
/path, where
path is the name of the file system in the ZFS namespace. Directories are created and destroyed as needed.
A file system can also have a mount point set in the
mountpoint property. This directory is created as needed, and ZFS automatically mounts the file system when the
zfs mount -a command is invoked (without editing
/etc/vfstab). The
mountpoint property can be inherited, so if
pool/home has a mount point of
/export/stuff, then
pool/home/user automatically inherits a mount point of
/export/stuff/user.
A file system
mountpoint property of
none prevents the file system from being mounted.
If needed, ZFS file systems can also be managed with traditional tools (
mount,
umount,
/etc/vfstab). If a file system's mount point is set to
legacy, ZFS makes no attempt to manage the file system, and the administrator is responsible for mounting and unmounting the file system.
Zones
A ZFS file system can be added to a non-global zone by using the
zonecfg add fs subcommand. A ZFS file system that is added to a non-global zone must have its
mountpoint property set to
legacy.
The physical properties of an added file system are controlled by the global administrator. However, the zone administrator can create, modify, or destroy files within the added file system, depending on how the file system is mounted.
A dataset can also be delegated to a non-global zone by using the
zonecfg add dataset subcommand. You cannot delegate a dataset to one zone and the children of the same dataset to another zone. The zone administrator can change properties of the dataset or any of its children. However, the
quota,
filesystem_limit and
snapshot_limit properties of the delegated dataset can be modified only by the global administrator.
A ZFS volume can be added as a device to a non-global zone by using the
zonecfg add device subcommand. However, its physical properties can be modified only by the global administrator.
For more information about
zonecfg syntax, see
zonecfg(1M).
After a dataset is delegated to a non-global zone, the
zoned property is automatically set. A zoned file system cannot be mounted in the global zone, since the zone administrator might have to set the mount point to an unacceptable value.
The global administrator can forcibly clear the
zoned property, though this should be done with extreme care. The global administrator should verify that all the mount points are acceptable before clearing the property.
Native Properties
Properties are divided into two types, native properties and user-defined (or “user”) properties. Native properties either export internal statistics or control ZFS behavior. In addition, native properties are either editable or read-only. User properties have no effect on ZFS behavior, but you can use them to annotate datasets in a way that is meaningful in your environment. For more information about user properties, see the
User Properties section, below.
Every dataset has a set of properties that export statistics about the dataset as well as control various behaviors. Properties are inherited from the parent unless overridden by the child. Some properties apply only to certain types of datasets (file systems, volumes, or snapshots).
The values of numeric properties can be specified using human-readable suffixes (for example,
k,
KB,
M,
Gb, and so forth, up to
Z for zettabyte). The following are all valid (and equal) specifications:
1536M, 1.5g, 1.50GB
.
The values of non-numeric properties are case sensitive and must be lowercase, except for
mountpoint,
sharenfs, and
sharesmb.
The following native properties consist of read-only statistics about the dataset. These properties can be neither set, nor inherited. Native properties apply to all dataset types unless otherwise noted.
-
available
-
The amount of space available to the dataset and all its children, assuming that there is no other activity in the pool. Because space is shared within a pool, availability can be limited by any number of factors, including physical pool size, quotas, reservations, or other datasets within the pool.
This property can also be referred to by its shortened column name, avail.
-
compressratio
-
For non-snapshots, the compression ratio achieved for the used space of this dataset, expressed as a multiplier. The used property includes descendant datasets, and, for clones, does not include the space shared with the origin snapshot. For snapshots, the compressratio is the same as the refcompressratio property. Compression can be turned on by running: zfs set compression=on dataset. The default value is off.
-
creation
-
The time this dataset was created.
-
clones
-
For snapshots, this property is a comma-separated list of filesystems or volumes which are clones of this snapshot. The clones' origin property is this snapshot. If the clones property is not empty, then this snapshot can not be destroyed (even with the -r or -f options).
-
defer_destroy
-
This property is on if the snapshot has been marked for deferred destroy by using the zfs destroy -d command. Otherwise, the property is off.
-
filesystem_count
-
The total number of filesystems and volumes that exist under this location in the dataset tree. This value is only available when a filesystem_limit has been set somewhere in the tree under which the dataset resides.
-
logicalreferenced
-
The amount of space that is “logically” accessible by this dataset. See the referenced property. The logical space ignores the effect of the compression and copies properties, giving a quantity closer to the amount of data that applications see. However, it does include space consumed by metadata.
This property can also be referred to by its shortened column name, lrefer.
-
logicalused
-
The amount of space that is “logically” consumed by this dataset and all its descendents. See the used property. The logical space ignores the effect of the compression and copies properties, giving a quantity closer to the amount of data that applications see. However, it does include space consumed by metadata.
This property can also be referred to by its shortened column name, lused.
-
mounted
-
For file systems, indicates whether the file system is currently mounted. This property can be either yes or no.
-
origin
-
For cloned file systems or volumes, the snapshot from which the clone was created. See also the clones property.
-
receive_resume_token
-
For filesystems or volumes which have saved partially-completed state from zfs receive -s, this opaque token can be provided to zfs send -t to resume and complete the zfs receive.
-
referenced
-
The amount of data that is accessible by this dataset, which may or may not be shared with other datasets in the pool. When a snapshot or clone is created, it initially references the same amount of space as the file system or snapshot it was created from, since its contents are identical.
This property can also be referred to by its shortened column name, refer.
-
refcompressratio
-
The compression ratio achieved for the referenced space of this dataset, expressed as a multiplier. See also the compressratio property.
-
snapshot_count
-
The total number of snapshots that exist under this location in the dataset tree. This value is only available when a snapshot_limit has been set somewhere in the tree under which the dataset resides.
-
type
-
The type of dataset: filesystem, volume, or snapshot.
-
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 are freed if this dataset is recursively destroyed, is the greater of its space used and its reservation.
When snapshots (see the Snapshots section) are created, their space is initially shared between the snapshot and the file system, and possibly with previous snapshots. As the file system changes, space that was previously shared becomes unique to the snapshot, and counted in the snapshot's space used. Additionally, deleting snapshots can increase the amount of space unique to (and used by) other snapshots.
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 fsync(3C) or O_SYNC does not necessarily guarantee that the space usage information is updated immediately.
-
usedby*
-
The usedby* properties decompose the used properties into the various reasons that space is used. Specifically, used
=
usedbychildren +
usedbydataset +
usedbyrefreservation +
usedbysnapshots. These properties are only available for datasets created on zpool “version 13” pools.
-
usedbychildren
-
The amount of space used by children of this dataset, which would be freed if all the dataset's children were destroyed.
-
usedbydataset
-
The amount of space used by this dataset itself, which would be freed if the dataset were destroyed (after first removing any refreservation and destroying any necessary snapshots or descendents).
-
usedbyrefreservation
-
The amount of space used by a refreservation set on this dataset, which would be freed if the refreservation was removed.
-
usedbysnapshots
-
The amount of space consumed by snapshots of this dataset. In particular, it is the amount of space that would be freed if all of this dataset's snapshots were destroyed. Note that this is not simply the sum of the snapshots' used properties because space can be shared by multiple snapshots.
-
userused@user
-
The amount of space consumed by the specified user in this dataset. Space is charged to the owner of each file, as displayed by ls -l. The amount of space charged is displayed by du and ls -s. See the zfs userspace subcommand for more information.
Unprivileged users can access only their own space usage. The root user, or a user who has been granted the userused privilege with zfs allow, can access everyone's usage.
The userused@... properties are not displayed by zfs get all. The user's name must be appended after the @ symbol, using one of the following forms:
-
POSIX name (for example, joe)
-
POSIX numeric ID (for example, 789)
-
SID name (for example, joe.smith@mydomain)
-
SID numeric ID (for example, S-1-123-456-789)
-
userrefs
-
This property is set to the number of user holds on this snapshot. User holds are set by using the zfs hold command.
-
groupused@group
-
The amount of space consumed by the specified group in this dataset. Space is charged to the group of each file, as displayed by ls -l. See the userused@user property for more information.
Unprivileged users can only access their own groups' space usage. The root user, or a user who has been granted the groupused privilege with zfs allow, can access all groups' usage.
-
volblocksize=blocksize
-
For volumes, specifies the block size of the volume. The blocksize cannot be changed once the volume has been written, so it should be set at volume creation time. The default blocksize for volumes is 8 Kbytes. Any power of 2 from 512 bytes to 128 Kbytes is valid.
This property can also be referred to by its shortened column name, volblock.
-
written
-
The amount of referenced space written to this dataset since the previous snapshot.
-
written@snapshot
-
The amount of referenced space written to this dataset since the specified snapshot. This is the space that is referenced by this dataset but was not referenced by the specified snapshot.
The snapshot may be specified as a short snapshot name (just the part after the @), in which case it will be interpreted as a snapshot in the same filesystem as this dataset. The snapshot may be a full snapshot name (filesystem@snapshot), which for clones may be a snapshot in the origin's filesystem (or the origin of the origin's filesystem, etc.)
The following native properties can be used to change the behavior of a ZFS dataset.
-
aclinherit=discard|noallow|restricted|passthrough|passthrough-x
-
Controls how ACEs are inherited when files and directories are created.
-
discard
-
does not inherit any ACEs.
-
noallow
-
only inherits inheritable ACEs that specify “deny” permissions.
-
restricted
-
default, removes the write_acl and write_owner permissions when the ACE is inherited.
-
passthrough
-
inherits all inheritable ACEs without any modifications.
-
passthrough-x
-
same meaning as passthrough, except that the owner@, group@, and everyone@ ACEs inherit the execute permission only if the file creation mode also requests the execute bit.
When the property value is set to passthrough, files are created with a mode determined by the inheritable ACEs. If no inheritable ACEs exist that affect the mode, then the mode is set in accordance to the requested mode from the application.
-
aclmode=discard|groupmask|passthrough|restricted
-
Controls how an ACL is modified during chmod(2).
-
discard
-
default, deletes all ACEs that do not represent the mode of the file.
-
groupmask
-
reduces permissions granted in all ALLOW entries found in the ACL such that they are no greater than the group permissions specified by chmod(2).
-
passthrough
-
indicates that no changes are made to the ACL other than creating or updating the necessary ACEs to represent the new mode of the file or directory.
-
restricted
-
causes the chmod(2) operation to return an error when used on any file or directory which has a non-trivial ACEs whose entries can not be represented by a mode.
chmod(2) is required to change the set user ID, set group ID, or sticky bits on a file or directory, as they do not have equivalent ACEs. In order to use chmod(2) on a file or directory with a non-trivial ACL when aclmode is set to restricted, you must first remove all ACEs which do not represent the current mode.
-
atime=on|off
-
Controls whether the access time for files is updated when they are read. Turning this property off avoids producing write traffic when reading files and can result in significant performance gains, though it might confuse mailers and other similar utilities. The default value is on.
-
canmount=on|off|noauto
-
If this property is set to off, the file system cannot be mounted, and is ignored by zfs mount -a. Setting this property to off is similar to setting the mountpoint property to none, except that the dataset still has a normal mountpoint property, which can be inherited. Setting this property to off allows datasets to be used solely as a mechanism to inherit properties. One example of setting canmount=off is to have two datasets with the same mountpoint, so that the children of both datasets appear in the same directory, but might have different inherited characteristics.
When set to noauto, a dataset can only be mounted and unmounted explicitly. The dataset is not mounted automatically when the dataset is created or imported, nor is it mounted by the zfs mount -a command or unmounted by the zfs unmount -a command.
This property is not inherited.
-
checksum=on|off|fletcher2|fletcher4|sha256|noparity|sha512|skein|edonr
-
Controls the checksum used to verify data integrity. The default value is on, which automatically selects an appropriate algorithm (currently, fletcher4, but this may change in future releases). The value off disables integrity checking on user data. The value noparity not only disables integrity but also disables maintaining parity for user data. This setting is used internally by a dump device residing on a RAID-Z pool and should not be used by any other dataset. Disabling checksums is NOT a recommended practice.
The sha512, skein, and edonr checksum algorithms require enabling the appropriate features on the pool. Please see zpool-features(5) for more information on these algorithms.
Changing this property affects only newly-written data.
-
compression=on|off|gzip|gzip-N|lz4|lzjb|zle
-
Controls the compression algorithm used for this dataset.
Setting compression to 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, 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 algorthm is either lzjb or, if the lz4_compress feature is enabled, lz4.
The lz4 compression algorithm is a high-performance replacement for the lzjb algorithm. It features significantly faster compression and decompression, as well as a moderately higher compression ratio than lzjb, but can only be used on pools with the lz4_compress feature set to enabled. See zpool-features(5) for details on ZFS feature flags and the lz4_compress feature.
The lzjb compression algorithm is optimized for performance while providing decent data compression.
The gzip compression algorithm uses the same compression as the gzip(1) command. You can specify the gzip level by using the value gzip-N, where N is an integer from 1 (fastest) to 9 (best compression ratio). Currently, gzip is equivalent to gzip-6 (which is also the default for gzip(1)).
The zle compression algorithm compresses runs of zeros.
This property can also be referred to by its shortened column name compress. Changing this property affects only newly-written data.
-
copies=1|2|3
-
Controls the number of copies of data stored for this dataset. These copies are in addition to any redundancy provided by the pool, for example, mirroring or RAID-Z. The copies are stored on different disks, if possible. The space used by multiple copies is charged to the associated file and dataset, changing the used property and counting against quotas and reservations.
Changing this property only affects newly-written data. Therefore, set this property at file system creation time by using the -o copies=N option.
-
devices=on|off
-
Controls whether device nodes can be opened on this file system. The default value is on.
-
exec=on|off
-
Controls whether processes can be executed from within this file system. The default value is on.
-
filesystem_limit=count|none
-
Limits the number of filesystems and volumes that can exist under this point in the dataset tree. The limit is not enforced if the user is allowed to change the limit. Setting a filesystem_limit to on a descendent of a filesystem that already has a filesystem_limit does not override the ancestor's filesystem_limit, but rather imposes an additional limit. This feature must be enabled to be used (see zpool-features(5)).
-
mountpoint=path|none|legacy
-
Controls the mount point used for this file system. See the Mount Points section for more information on how this property is used.
When the mountpoint property is changed for a file system, the file system and any children that inherit the mount point are unmounted. If the new value is legacy, then they remain unmounted. Otherwise, they are automatically remounted in the new location if the property was previously legacy or none, or if they were mounted before the property was changed. In addition, any shared file systems are unshared and shared in the new location.
-
nbmand=on|off
-
Controls whether the file system should be mounted with nbmand (Non Blocking mandatory locks). This is used for SMB clients. Changes to this property only take effect when the file system is umounted and remounted. See mount(1M) for more information on nbmand mounts.
-
primarycache=all|none|metadata
-
Controls what is cached in the primary cache (ARC). If this property is set to all, then both user data and metadata is cached. If this property is set to none, then neither user data nor metadata is cached. If this property is set to metadata, then only metadata is cached. The default value is all.
-
quota=size|none
-
Limits the amount of space a dataset and its descendents can consume. This property enforces a hard limit on the amount of space used. This includes all space consumed by descendents, including file systems and snapshots. Setting a quota on a descendent of a dataset that already has a quota does not override the ancestor's quota, but rather imposes an additional limit.
Quotas cannot be set on volumes, as the volsize property acts as an implicit quota.
-
snapshot_limit=count|none
-
Limits the number of snapshots that can be created on a dataset and its descendents. Setting a snapshot_limit on a descendent of a dataset that already has a snapshot_limit does not override the ancestor's snapshot_limit, but rather imposes an additional limit. The limit is not enforced if the user is allowed to change the limit. For example, this means that recursive snapshots taken from the global zone are counted against each delegated dataset within a zone. This feature must be enabled to be used (see zpool-features(5)).
-
userquota@user=size|none
-
Limits the amount of space consumed by the specified user. User space consumption is identified by the userspace@user property.
Enforcement of user quotas may be delayed by several seconds. This delay means that a user might exceed their quota before the system notices that they are over quota and begins to refuse additional writes with the EDQUOT error message. See the zfs userspace subcommand for more information.
Unprivileged users can only access their own groups' space usage. The root user, or a user who has been granted the userquota privilege with zfs allow, can get and set everyone's quota.
This property is not available on volumes, on file systems before version 4, or on pools before version 15. The userquota@... properties are not displayed by zfs get all. The user's name must be appended after the @ symbol, using one of the following forms:
-
POSIX name (for example, joe)
-
POSIX numeric ID (for example, 789)
-
SID name (for example, joe.smith@mydomain)
-
SID numeric ID (for example, S-1-123-456-789)
-
groupquota@group=size|none
-
Limits the amount of space consumed by the specified group. Group space consumption is identified by the groupused@group property.
Unprivileged users can access only their own groups' space usage. The root user, or a user who has been granted the groupquota privilege with zfs allow, can get and set all groups' quotas.
-
readonly=on|off
-
Controls whether this dataset can be modified. The default value is off.
This property can also be referred to by its shortened column name, rdonly.
-
recordsize=size
-
Specifies a suggested block size for files in the file system. This property is designed solely for use with database workloads that access files in fixed-size records. ZFS automatically tunes block sizes according to internal algorithms optimized for typical access patterns.
For databases that create very large files but access them in small random chunks, these algorithms may be suboptimal. Specifying a recordsize greater than or equal to the record size of the database can result in significant performance gains. Use of this property for general purpose file systems is strongly discouraged, and may adversely affect performance.
The size specified must be a power of two greater than or equal to 512 and less than or equal to 128 Kbytes. If the large_blocks feature is enabled on the pool, the size may be up to 1 Mbyte. See zpool-features(5) for details on ZFS feature flags.
Changing the file system's recordsize affects only files created afterward; existing files are unaffected.
This property can also be referred to by its shortened column name, recsize.
-
redundant_metadata=all|most
-
Controls what types of metadata are stored redundantly. ZFS stores an extra copy of metadata, so that if a single block is corrupted, the amount of user data lost is limited. This extra copy is in addition to any redundancy provided at the pool level (e.g. by mirroring or RAID-Z), and is in addition to an extra copy specified by the copies property (up to a total of 3 copies). For example if the pool is mirrored, copies=2, and redundant_metadata=most, then ZFS stores 6 copies of most metadata, and 4 copies of data and some metadata.
When set to all, ZFS stores an extra copy of all metadata. If a single on-disk block is corrupt, at worst a single block of user data (which is recordsize bytes long) can be lost.
When set to most, ZFS stores an extra copy of most types of metadata. This can improve performance of random writes, because less metadata must be written. In practice, at worst about 100 blocks (of recordsize bytes each) of user data can be lost if a single on-disk block is corrupt. The exact behavior of which metadata blocks are stored redundantly may change in future releases.
The default value is all.
-
refquota=size|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.
-
refreservation=size|none
-
The minimum amount of space guaranteed to a dataset, not including its descendents. When the amount of space used is below this value, the dataset is treated as if it were taking up the amount of space specified by refreservation. The refreservation reservation is accounted for in the parent datasets' space used, and counts against the parent datasets' quotas and reservations.
If refreservation is set, a snapshot is only allowed if there is enough free pool space outside of this reservation to accommodate the current number of “referenced” bytes in the dataset.
This property can also be referred to by its shortened column name, refreserv.
-
reservation=size|none
-
The minimum amount of space guaranteed to a dataset and 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 its reservation. Reservations are accounted for in the parent datasets' space used, and count against the parent datasets' quotas and reservations.
This property can also be referred to by its shortened column name, reserv.
-
secondarycache=all|none|metadata
-
Controls what is cached in the secondary cache (L2ARC). If this property is set to all, then both user data and metadata is cached. If this property is set to none, then neither user data nor metadata is cached. If this property is set to metadata, then only metadata is cached. The default value is all.
-
setuid=on|off
-
Controls whether the setuid bit is respected for the file system. The default value is on.
-
sharesmb=on|off|opts
-
Controls whether the file system is shared via SMB, and what options are to be used. A file system with the sharesmb property set to off is managed through traditional tools such as sharemgr(1M). Otherwise, the file system is automatically shared and unshared with the zfs share and zfs unshare commands. If the property is set to on, the sharemgr(1M) command is invoked with no options. Otherwise, the sharemgr(1M) command is invoked with options equivalent to the contents of this property.
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 illegal in the resource name, are replaced with underscore (_) characters. A pseudo property “name” is also supported that allows you to replace the data set name with a specified name. The specified name is then used to replace the prefix dataset in the case of inheritance. For example, if the dataset data/home/john is set to name=john, then data/home/john has a resource name of john. If a child dataset data/home/john/backups is shared, it has a resource name of john_backups.
When SMB shares are created, the SMB share name appears as an entry in the .zfs/shares directory. You can use the ls or chmod command to display the share-level ACLs on the entries in this directory.
When the sharesmb 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 set to off, or if they were shared before the property was changed. If the new property is set to off, the file systems are unshared.
-
sharenfs=on|off|opts
-
Controls whether the file system is shared via NFS, and what options are to be used. A file system with a sharenfs property of off is managed through traditional tools such as share(1M), unshare(1M), and dfstab(4). Otherwise, the file system is automatically shared and unshared with the zfs share and zfs unshare commands. If the property is set to on, share(1M) command is invoked with no options. Otherwise, the share(1M) command is invoked with options equivalent to the contents of this property.
When the sharenfs property is changed for a dataset, the dataset and any children inheriting the property are re-shared with the new options, only if the property was previously off, or if they were shared before the property was changed. If the new property is off, the file systems are unshared.
-
logbias=latency|throughput
-
Provide a hint to ZFS about handling of synchronous requests in this dataset. If logbias is set to latency (the default), ZFS will use pool log devices (if configured) to handle the requests at low latency. If logbias is set to throughput, ZFS will not use configured pool log devices. ZFS will instead optimize synchronous operations for global pool throughput and efficient use of resources.
-
snapdir=hidden|visible
-
Controls whether the .zfs directory is hidden or visible in the root of the file system as discussed in the Snapshots section. The default value is hidden.
-
sync=standard|always|disabled
-
Controls the behavior of synchronous requests (e.g. fsync, O_DSYNC). standard is the POSIX specified behavior of ensuring all synchronous requests are written to stable storage and all devices are flushed to ensure data is not cached by device controllers (this is the default). always causes every file system transaction to be written and flushed before its system call returns. This has a large performance penalty. disabled disables synchronous requests. File system transactions are only committed to stable storage periodically. This option will give the highest performance. However, it is very dangerous as ZFS would be ignoring the synchronous transaction demands of applications such as databases or NFS. Administrators should only use this option when the risks are understood.
-
version=N|current
-
The on-disk version of this file system, which is independent of the pool version. This property can only be set to later supported versions. See the zfs upgrade command.
-
volsize=size
-
For volumes, specifies the logical size of the volume. By default, creating a volume establishes a reservation of equal size. For storage pools with a version number of 9 or higher, a refreservation is set instead. Any changes to volsize are reflected in an equivalent change to the reservation (or refreservation). The volsize can only be set to a multiple of volblocksize, and cannot be zero.
The reservation is kept equal to the volume's logical size to prevent unexpected behavior for consumers. Without the reservation, the 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 (particularly when shrinking the size). Extreme care should be used when adjusting the volume size.
Though not recommended, a “sparse volume” (also known as “thin provisioning”) can be created by specifying the -s option to the zfs create -V command, or by changing the reservation after the volume has been created. A “sparse volume” is a volume where the reservation is less then the volume size. Consequently, writes to a sparse volume can fail with ENOSPC when the pool is low on space. For a sparse volume, changes to volsize are not reflected in the reservation.
-
vscan=on|off
-
Controls whether regular files should be scanned for viruses when a file is opened and closed. In addition to enabling this property, the virus scan service must also be enabled for virus scanning to occur. The default value is off.
-
xattr=on|off
-
Controls whether extended attributes are enabled for this file system. The default value is on.
-
zoned=on|off
-
Controls whether the dataset is managed from a non-global zone. See the Zones section for more information. The default value is off.
The following three properties cannot be changed after the file system is created, and therefore, should be set when the file system is created. If the properties are not set with the
zfs create or
zpool create 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.
-
casesensitivity=sensitive|insensitive|mixed
-
Indicates whether the file name matching algorithm used by the file system should be case-sensitive, case-insensitive, or allow a combination of both styles of matching. The default value for the casesensitivity property is sensitive. Traditionally, UNIX and POSIX file systems have case-sensitive file names.
The mixed value for the casesensitivity property indicates that the file system can support requests for both case-sensitive and case-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 mixed value behavior, see the "ZFS Administration Guide".
-
normalization=none|formC|formD|formKC|formKD
-
Indicates whether the file system should perform a 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 none, and the utf8only property was left unspecified, the utf8only property is automatically set to on. The default value of the normalization property is none. This property cannot be changed after the file system is created.
-
utf8only=on|off
-
Indicates whether the file system should reject file names that include characters that are not present in the UTF-8 character code set. If this property is explicitly set to off, the normalization property must either not be explicitly set or be set to none. The default value for the utf8only property is off. This property cannot be changed after the file system is created.
The
casesensitivity,
normalization, and
utf8only properties are also new permissions that can be assigned to non-privileged users by using the ZFS delegated administration feature.
Temporary Mount Point Properties
When a file system is mounted, either through
mount(1M) for legacy mounts or the
zfs mount command for normal file systems, its mount options are set according to its properties. The correlation between properties and mount options is as follows:
PROPERTY MOUNT OPTION
devices devices/nodevices
exec exec/noexec
readonly ro/rw
setuid setuid/nosetuid
xattr xattr/noxattr
In addition, these options can be set on a per-mount basis using the
-o option, without affecting the property that is stored on disk. The values specified on the command line override the values stored in the dataset. The
nosuid option is an alias for
nodevices,
nosetuid. These properties are reported as “temporary” by the
zfs get command. If the properties are changed while the dataset is mounted, the new setting overrides any temporary settings.
User Properties
In addition to the standard native properties, ZFS supports arbitrary user properties. User properties have no effect on ZFS behavior, but applications or administrators can use them to annotate datasets (file systems, volumes, and snapshots).
User property names must contain a colon (“
:”) character to distinguish them from native properties. They may contain lowercase letters, numbers, and the following punctuation characters: colon (“
:”), dash (“
-”), period (“
.”), and underscore (“
_”). The expected convention is that the property name is divided into two portions such as
module:
property, but this namespace is not enforced by ZFS. User property names can be at most 256 characters, and cannot begin with a dash (“
-”).
When making programmatic use of user properties, it is strongly suggested to use a reversed
DNS domain name for the
module component of property names to reduce the chance that two independently-developed packages use the same property name for different purposes.
The values of user properties are arbitrary strings, are always inherited, and are never validated. All of the commands that operate on properties (
zfs list,
zfs get,
zfs set, and so forth) can be used to manipulate both native properties and user properties. Use the
zfs inherit command to clear a user property . If the property is not defined in any parent dataset, it is removed entirely. Property values are limited to 1024 characters.
ZFS Volumes as Swap or Dump Devices
During an initial installation a swap device and dump device are created on ZFS volumes in the ZFS root pool. By default, the swap area size is based on 1/2 the size of physical memory up to 2 Gbytes. The size of the dump device depends on the kernel's requirements at installation time. Separate ZFS volumes must be used for the swap area and dump devices. Do not swap to a file on a ZFS file system. A ZFS swap file configuration is not supported.
If you need to change your swap area or dump device after the system is installed or upgraded, use the
swap(1M) and
dumpadm(1M) commands.