ZPOOL-FEATURES(7)

NAME
zpool-features - ZFS pool feature descriptions

DESCRIPTION
ZFS pool on-disk format versions are specified via "features" which replace the old on-disk format numbers (the last supported on-disk format number is 28). To enable a feature on a pool use the upgrade subcommand of the zpool(8) command, or set the feature@feature_name property to enabled.

The pool format does not affect file system version compatibility or the ability to send file systems between pools.

Since most features can be enabled independently of each other the on-disk format of the pool is specified by the set of all features marked as active on the pool. If the pool was created by another software version this set may include unsupported features.

  Identifying features
Every feature has a guid of the form com.example:feature_name. The reverse DNS name ensures that the feature's guid is unique across all ZFS implementations. When unsupported features are encountered on a pool they will be identified by their guids. Refer to the documentation for the ZFS implementation that created the pool for information about those features.

Each supported feature also has a short name. By convention a feature's short name is the portion of its guid which follows the ':' (e.g. com.example:feature_name would have the short name feature_name ), however a feature's short name may differ across ZFS implementations if following the convention would result in name conflicts.

  Feature states
Features can be in one of three states:

active
    This feature's on-disk format changes are in effect on the pool. Support for this feature is required to import the pool in read-write mode. If this feature is not read-only compatible, support is also required to import the pool in read-only mode (see "Read-only compatibility").

enabled
    An administrator has marked this feature as enabled on the pool, but the feature's on-disk format changes have not been made yet. The pool can still be imported by software that does not support this feature, but changes may be made to the on-disk format at any time which will move the feature to the active state. Some features may support returning to the enabled state after becoming active. See feature-specific documentation for details.

disabled
    This feature's on-disk format changes have not been made and will not be made unless an administrator moves the feature to the enabled state. Features cannot be disabled once they have been enabled.

The state of supported features is exposed through pool properties of the form feature@short_name.

  Read-only compatibility
Some features may make on-disk format changes that do not interfere with other software's ability to read from the pool. These features are referred to as "read-only compatible". If all unsupported features on a pool are read-only compatible, the pool can be imported in read-only mode by setting the readonly property during import (see zpool(8) for details on importing pools).

  Unsupported features
For each unsupported feature enabled on an imported pool a pool property named unsupported@feature_guid will indicate why the import was allowed despite the unsupported feature. Possible values for this property are:

inactive
    The feature is in the enabled state and therefore the pool's on-disk format is still compatible with software that does not support this feature.

readonly
    The feature is read-only compatible and the pool has been imported in read-only mode.

  Feature dependencies
Some features depend on other features being enabled in order to function properly. Enabling a feature will automatically enable any features it depends on.

FEATURES
The following features are supported on this system:

async_destroy
    GUID | com.delphix:async_destroy
    READ-ONLY COMPATIBLE | yes
    DEPENDENCIES | none

    Destroying a file system requires traversing all of its data in order to return its used space to the pool. Without async_destroy the file system is not fully removed until all space has been reclaimed. If the destroy operation is interrupted by a reboot or power outage the next attempt to open the pool will need to complete the destroy operation synchronously.

    When async_destroy is enabled the file system's data will be reclaimed by a background process, allowing the destroy operation to complete without traversing the entire file system. The background process is able to resume interrupted destroys after the pool has been opened, eliminating the need to finish interrupted destroys as part of the open operation. The amount of space remaining to be reclaimed by the background process is available through the freeing property.

    This feature is only active while freeing is non-zero.

empty_bpobj
    GUID | com.delphix:empty_bpobj
    READ-ONLY COMPATIBLE | yes
    DEPENDENCIES | none

    This feature increases the performance of creating and using a large number of snapshots of a single filesystem or volume, and also reduces the disk space required.

    When there are many snapshots, each snapshot uses many Block Pointer Objects (bpobj's) to track blocks associated with that snapshot. However, in common use cases, most of these bpobj's are empty. This feature allows us to create each bpobj on-demand, thus eliminating the empty bpobjs.

    This feature is active while there are any filesystems, volumes, or snapshots which were created after enabling this feature.

lz4_compress
    GUID | org.illumos:lz4_compress
    READ-ONLY COMPATIBLE | no
    DEPENDENCIES | none

    lz4 is a high-performance real-time compression algorithm that features significantly faster compression and decompression as well as a higher compression ratio than the older lzjb compression. Typically, lz4 compression is approximately 50% faster on compressible data and 200% faster on incompressible data than lzjb. It is also approximately 80% faster on decompression, while giving approximately 10% better compression ratio.

    When the lz4_compress feature is set to enabled, the administrator can turn on lz4 compression on any dataset on the pool using the zfs(8) command. Please note that doing so will immediately activate the lz4_compress feature on the underlying pool (even before any data is written). Since this feature is not read-only compatible, this operation will render the pool unimportable on systems without support for the lz4_compress feature. At the moment, this operation cannot be reversed. Booting off of lz4 -compressed root pools is supported.

SEE ALSO
zpool(8)

AUTHORS
This manual page is a mdoc(7) reimplementation of the illumos manual page zpool-features(5), modified and customized for FreeBSD and licensed under the Common Development and Distribution License (CDDL).

The mdoc(7) implementation of this manual page was initially written by Martin Matuska <mm@FreeBSD.org>.