'\" te .\" Copyright (c) 2013 by Delphix. All rights reserved. .\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved. .\" Copyright (c) 2013, Joyent, Inc. All rights reserved. .\" 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. When distributing Covered Code, include this .\" CDDL HEADER in each file and include the License file at .\" usr/src/OPENSOLARIS.LICENSE. 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] .TH ZPOOL-FEATURES 5 "Aug 27, 2013" .SH NAME zpool\-features \- ZFS pool feature descriptions .SH DESCRIPTION .sp .LP 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 \fBupgrade\fR subcommand of the \fBzpool\fR(1M) command, or set the \fBfeature@\fR\fIfeature_name\fR property to \fBenabled\fR. .sp .LP The pool format does not affect file system version compatibility or the ability to send file systems between pools. .sp .LP 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 \fBactive\fR on the pool. If the pool was created by another software version this set may include unsupported features. .SS "Identifying features" .sp .LP Every feature has a guid of the form \fIcom.example:feature_name\fR. 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. .sp .LP 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. \fIcom.example:feature_name\fR would have the short name \fIfeature_name\fR), however a feature's short name may differ across ZFS implementations if following the convention would result in name conflicts. .SS "Feature states" .sp .LP Features can be in one of three states: .sp .ne 2 .na \fB\fBactive\fR\fR .ad .RS 12n 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"). .RE .sp .ne 2 .na \fB\fBenabled\fR\fR .ad .RS 12n 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 \fBactive\fR state. Some features may support returning to the \fBenabled\fR state after becoming \fBactive\fR. See feature\-specific documentation for details. .RE .sp .ne 2 .na \fBdisabled\fR .ad .RS 12n This feature's on\-disk format changes have not been made and will not be made unless an administrator moves the feature to the \fBenabled\fR state. Features cannot be disabled once they have been enabled. .RE .sp .LP The state of supported features is exposed through pool properties of the form \fIfeature@short_name\fR. .SS "Read\-only compatibility" .sp .LP 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 \fBreadonly\fR property during import (see \fBzpool\fR(1M) for details on importing pools). .SS "Unsupported features" .sp .LP For each unsupported feature enabled on an imported pool a pool property named \fIunsupported@feature_guid\fR will indicate why the import was allowed despite the unsupported feature. Possible values for this property are: .sp .ne 2 .na \fB\fBinactive\fR\fR .ad .RS 12n The feature is in the \fBenabled\fR state and therefore the pool's on\-disk format is still compatible with software that does not support this feature. .RE .sp .ne 2 .na \fB\fBreadonly\fR\fR .ad .RS 12n The feature is read\-only compatible and the pool has been imported in read\-only mode. .RE .SS "Feature dependencies" .sp .LP Some features depend on other features being enabled in order to function properly. Enabling a feature will automatically enable any features it depends on. .SH FEATURES .sp .LP The following features are supported on this system: .sp .ne 2 .na \fB\fBasync_destroy\fR\fR .ad .RS 4n .TS l l . GUID com.delphix:async_destroy READ\-ONLY COMPATIBLE yes DEPENDENCIES none .TE Destroying a file system requires traversing all of its data in order to return its used space to the pool. Without \fBasync_destroy\fR 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 \fBasync_destroy\fR 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 \fBfreeing\fR property. This feature is only \fBactive\fR while \fBfreeing\fR is non\-zero. .RE .sp .ne 2 .na \fB\fBempty_bpobj\fR\fR .ad .RS 4n .TS l l . GUID com.delphix:empty_bpobj READ\-ONLY COMPATIBLE yes DEPENDENCIES none .TE 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 \fBactive\fR while there are any filesystems, volumes, or snapshots which were created after enabling this feature. .RE .sp .ne 2 .na \fB\fBlz4_compress\fR\fR .ad .RS 4n .TS l l . GUID org.illumos:lz4_compress READ\-ONLY COMPATIBLE no DEPENDENCIES none .TE \fBlz4\fR 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 \fBlzjb\fR compression. Typically, \fBlz4\fR compression is approximately 50% faster on compressible data and 200% faster on incompressible data than \fBlzjb\fR. It is also approximately 80% faster on decompression, while giving approximately 10% better compression ratio. When the \fBlz4_compress\fR feature is set to \fBenabled\fR, the administrator can turn on \fBlz4\fR compression on any dataset on the pool using the \fBzfs\fR(1M) command. Please note that doing so will immediately activate the \fBlz4_compress\fR 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 \fBlz4_compress\fR feature. At the moment, this operation cannot be reversed. Booting off of \fBlz4\fR-compressed root pools is supported. .RE .sp .ne 2 .na \fB\fBspacemap_histogram\fR\fR .ad .RS 4n .TS l l . GUID com.delphix:spacemap_histogram READ\-ONLY COMPATIBLE yes DEPENDENCIES none .TE This features allows ZFS to maintain more information about how free space is organized within the pool. If this feature is \fBenabled\fR, ZFS will set this feature to \fBactive\fR when a new space map object is created or an existing space map is upgraded to the new format. Once the feature is \fBactive\fR, it will remain in that state until the pool is destroyed. .RE .sp .ne 2 .na \fB\fBmulti_vdev_crash_dump\fR\fR .ad .RS 4n .TS l l . GUID com.joyent:multi_vdev_crash_dump READ\-ONLY COMPATIBLE no DEPENDENCIES none .TE 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 \fBmulti_vdev_crash_dump\fR feature is set to \fBenabled\fR, the administrator can use the \fBdumpadm\fR(1M) command to configure a dump device on a pool comprised of multiple vdevs. .RE .sp .ne 2 .na \fB\fBextensible_dataset\fR\fR .ad .RS 4n .TS l l . GUID com.delphix:extensible_dataset READ\-ONLY COMPATIBLE no DEPENDENCIES none .TE This feature allows more flexible use of internal ZFS data structures, and exists for other features to depend on. This feature will be \fBactive\fR when the first dependent feature uses it, and will be returned to the \fBenabled\fR state when all datasets that use this feature are destroyed. .RE .SH "SEE ALSO" \fBzpool\fR(1M)