man/man5/zpool-features.5

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 ZPOOL-FEATURES 5 "Aug 27, 2013"
 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(1M) 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(1M) 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(1M) 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.


spacemap_histogram


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


This features allows ZFS to maintain more information about how free space
is organized within the pool. If this feature is enabled, ZFS will
set this feature to active when a new space map object is created or
an existing space map is upgraded to the new format. Once the feature is
active, it will remain in that state until the pool is destroyed.


multi_vdev_crash_dump


GUID com.joyent:multi_vdev_crash_dump
READ-ONLY COMPATIBLE no
DEPENDENCIES none


This feature allows a dump device to be configured with a pool comprised
of multiple vdevs. Those vdevs may be arranged in any mirrored or raidz
configuration.

When the multi_vdev_crash_dump feature is set to enabled,
the administrator can use the dumpadm(1M) command to configure a
dump device on a pool comprised of multiple vdevs.


extensible_dataset


GUID com.delphix:extensible_dataset
READ-ONLY COMPATIBLE no
DEPENDENCIES none


This feature allows more flexible use of internal ZFS data structures,
and exists for other features to depend on.

This feature will be active when the first dependent feature uses it,
and will be returned to the enabled state when all datasets that use
this feature are destroyed.


 "SEE ALSO"
zpool(1M)