Skip site navigation (1)Skip section navigation (2)

FreeBSD Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
ZPOOL-FEATURES(7)  FreeBSD Miscellaneous Information Manual  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>.

FreeBSD 11.0-PRERELEASE        February 8, 2013        FreeBSD 11.0-PRERELEASE

NAME | DESCRIPTION | FEATURES | SEE ALSO | AUTHORS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=zpool-features&sektion=7&manpath=FreeBSD+9.2-RELEASE>

home | help