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diff --git a/usr/src/man/man7/zpool-features.7 b/usr/src/man/man7/zpool-features.7 new file mode 100644 index 0000000000..146bfc5262 --- /dev/null +++ b/usr/src/man/man7/zpool-features.7 @@ -0,0 +1,835 @@ +'\" te +.\" Copyright (c) 2013, 2017 by Delphix. All rights reserved. +.\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved. +.\" Copyright (c) 2014, Joyent, Inc. All rights reserved. +.\" Copyright (c) 2014 Integros [integros.com] +.\" 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 7 "May 15, 2019" +.SH NAME +zpool\-features \- ZFS pool feature descriptions +.SH DESCRIPTION +.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(8) 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" +.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" +.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" +.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(8) for details on +importing pools). +.SS "Unsupported features" +.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" +.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 +.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\fBfilesystem_limits\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.joyent:filesystem_limits +READ\-ONLY COMPATIBLE yes +DEPENDENCIES extensible_dataset +.TE + +This feature enables filesystem and snapshot limits. These limits can be used +to control how many filesystems and/or snapshots can be created at the point in +the tree on which the limits are set. + +This feature is \fBactive\fR once either of the limit properties has been +set on a dataset. Once activated the feature is never deactivated. +.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(8) command. Also, all newly written metadata +will be compressed with \fBlz4\fR algorithm. 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. Booting +off of \fBlz4\fR-compressed root pools is supported. + +This feature becomes \fBactive\fR as soon as it is enabled and will +never return to being \fBenabled\fR. +.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(8) 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 + +.sp +.ne 2 +.na +\fB\fBbookmarks\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.delphix:bookmarks +READ\-ONLY COMPATIBLE yes +DEPENDENCIES extensible_dataset +.TE + +This feature enables use of the \fBzfs bookmark\fR subcommand. + +This feature is \fBactive\fR while any bookmarks exist in the pool. +All bookmarks in the pool can be listed by running +\fBzfs list -t bookmark -r \fIpoolname\fR\fR. + +.RE + +.sp +.ne 2 +.na +\fB\fBenabled_txg\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.delphix:enabled_txg +READ\-ONLY COMPATIBLE yes +DEPENDENCIES none +.TE + +Once this feature is enabled ZFS records the transaction group number +in which new features are enabled. This has no user-visible impact, +but other features may depend on this feature. + +This feature becomes \fBactive\fR as soon as it is enabled and will +never return to being \fBenabled\fR. + +.RE + +.sp +.ne 2 +.na +\fB\fBhole_birth\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.delphix:hole_birth +READ\-ONLY COMPATIBLE no +DEPENDENCIES enabled_txg +.TE + +This feature improves performance of incremental sends ("zfs send -i") +and receives for objects with many holes. The most common case of +hole-filled objects is zvols. + +An incremental send stream from snapshot \fBA\fR to snapshot \fBB\fR +contains information about every block that changed between \fBA\fR and +\fBB\fR. Blocks which did not change between those snapshots can be +identified and omitted from the stream using a piece of metadata called +the 'block birth time', but birth times are not recorded for holes (blocks +filled only with zeroes). Since holes created after \fBA\fR cannot be +distinguished from holes created before \fBA\fR, information about every +hole in the entire filesystem or zvol is included in the send stream. + +For workloads where holes are rare this is not a problem. However, when +incrementally replicating filesystems or zvols with many holes (for +example a zvol formatted with another filesystem) a lot of time will +be spent sending and receiving unnecessary information about holes that +already exist on the receiving side. + +Once the \fBhole_birth\fR feature has been enabled the block birth times +of all new holes will be recorded. Incremental sends between snapshots +created after this feature is enabled will use this new metadata to avoid +sending information about holes that already exist on the receiving side. + +This feature becomes \fBactive\fR as soon as it is enabled and will +never return to being \fBenabled\fR. + +.RE + +.sp +.ne 2 +.na +\fB\fBembedded_data\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.delphix:embedded_data +READ\-ONLY COMPATIBLE no +DEPENDENCIES none +.TE + +This feature improves the performance and compression ratio of +highly-compressible blocks. Blocks whose contents can compress to 112 bytes +or smaller can take advantage of this feature. + +When this feature is enabled, the contents of highly-compressible blocks are +stored in the block "pointer" itself (a misnomer in this case, as it contains +the compresseed data, rather than a pointer to its location on disk). Thus +the space of the block (one sector, typically 512 bytes or 4KB) is saved, +and no additional i/o is needed to read and write the data block. + +This feature becomes \fBactive\fR as soon as it is enabled and will +never return to being \fBenabled\fR. + +.RE +.sp +.ne 2 +.na +\fB\fBdevice_removal\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.delphix:device_removal +READ\-ONLY COMPATIBLE no +DEPENDENCIES none +.TE + +This feature enables the "zpool remove" subcommand to remove top-level +vdevs, evacuating them to reduce the total size of the pool. + +This feature becomes \fBactive\fR when the "zpool remove" command is used +on a top-level vdev, and will never return to being \fBenabled\fR. + +.RE +.sp +.ne 2 +.na +\fB\fBobsolete_counts\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.delphix:obsolete_counts +READ\-ONLY COMPATIBLE yes +DEPENDENCIES device_removal +.TE + +This feature is an enhancement of device_removal, which will over time +reduce the memory used to track removed devices. When indirect blocks +are freed or remapped, we note that their part of the indirect mapping +is "obsolete", i.e. no longer needed. See also the \fBzfs remap\fR +subcommand in \fBzfs\fR(8). + +This feature becomes \fBactive\fR when the "zpool remove" command is +used on a top-level vdev, and will never return to being \fBenabled\fR. + +.RE +.sp +.ne 2 +.na +\fB\fBzpool_checkpoint\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.delphix:zpool_checkpoint +READ\-ONLY COMPATIBLE yes +DEPENDENCIES none +.TE + +This feature enables the "zpool checkpoint" subcommand that can +checkpoint the state of the pool at the time it was issued and later +rewind back to it or discard it. + +This feature becomes \fBactive\fR when the "zpool checkpoint" command +is used to checkpoint the pool. +The feature will only return back to being \fBenabled\fR when the pool +is rewound or the checkpoint has been discarded. + +.RE +.sp +.ne 2 +.na +\fB\fBspacemap_v2\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.delphix:spacemap_v2 +READ\-ONLY COMPATIBLE yes +DEPENDENCIES none +.TE + +This feature enables the use of the new space map encoding which +consists of two words (instead of one) whenever it is advantageous. +The new encoding allows space maps to represent large regions of +space more efficiently on-disk while also increasing their maximum +addressable offset. + +This feature becomes \fBactive\fR once it is \fBenabled\fR, and never +returns back to being \fBenabled\fR. + +.RE +.sp +.ne 2 +.na +\fB\fBlarge_blocks\fR\fR +.ad +.RS 4n +.TS +l l . +GUID org.open-zfs:large_block +READ\-ONLY COMPATIBLE no +DEPENDENCIES extensible_dataset +.TE + +The \fBlarge_block\fR feature allows the record size on a dataset to be +set larger than 128KB. + +This feature becomes \fBactive\fR once a \fBrecordsize\fR property has been +set larger than 128KB, and will return to being \fBenabled\fR once all +filesystems that have ever had their recordsize larger than 128KB are destroyed. +.RE + +.ne 2 +.na +\fB\fBlarge_dnode\fR\fR +.ad +.RS 4n +.TS +l l . +GUID org.zfsonlinux:large_dnode +READ\-ONLY COMPATIBLE no +DEPENDENCIES extensible_dataset +.TE + +The \fBlarge_dnode\fR feature allows the size of dnodes in a dataset to be +set larger than 512B. + +This feature becomes \fBactive\fR once a dataset contains an object with a +dnode larger than 512B, which occurs as a result of setting the \fBdnodesize\fR +dataset property to a value other than \fBlegacy\fR. The feature will return to +being \fBenabled\fR once all filesystems that have ever contained a dnode larger +than 512B are destroyed. Large dnodes allow more data to be stored in the +bonus buffer, thus potentially improving performance by avoiding the use of +spill blocks. +.RE + +.sp +.ne 2 +.na +\fB\fBsha512\fR\fR +.ad +.RS 4n +.TS +l l . +GUID org.illumos:sha512 +READ\-ONLY COMPATIBLE no +DEPENDENCIES extensible_dataset +.TE + +This feature enables the use of the SHA-512/256 truncated hash algorithm +(FIPS 180-4) for checksum and dedup. The native 64-bit arithmetic of +SHA-512 provides an approximate 50% performance boost over SHA-256 on +64-bit hardware and is thus a good minimum-change replacement candidate +for systems where hash performance is important, but these systems +cannot for whatever reason utilize the faster \fBskein\fR and +\fBedonr\fR algorithms. + +When the \fBsha512\fR feature is set to \fBenabled\fR, the administrator +can turn on the \fBsha512\fR checksum on any dataset using the +\fBzfs set checksum=sha512\fR command. This feature becomes +\fBactive\fR once a \fBchecksum\fR property has been set to \fBsha512\fR, +and will return to being \fBenabled\fR once all filesystems that have +ever had their checksum set to \fBsha512\fR are destroyed. + +Booting off of pools utilizing SHA-512/256 is supported. + +.RE + +.sp +.ne 2 +.na +\fB\fBskein\fR\fR +.ad +.RS 4n +.TS +l l . +GUID org.illumos:skein +READ\-ONLY COMPATIBLE no +DEPENDENCIES extensible_dataset +.TE + +This feature enables the use of the Skein hash algorithm for checksum +and dedup. Skein is a high-performance secure hash algorithm that was a +finalist in the NIST SHA-3 competition. It provides a very high security +margin and high performance on 64-bit hardware (80% faster than +SHA-256). This implementation also utilizes the new salted checksumming +functionality in ZFS, which means that the checksum is pre-seeded with a +secret 256-bit random key (stored on the pool) before being fed the data +block to be checksummed. Thus the produced checksums are unique to a +given pool, preventing hash collision attacks on systems with dedup. + +When the \fBskein\fR feature is set to \fBenabled\fR, the administrator +can turn on the \fBskein\fR checksum on any dataset using the +\fBzfs set checksum=skein\fR command. This feature becomes +\fBactive\fR once a \fBchecksum\fR property has been set to \fBskein\fR, +and will return to being \fBenabled\fR once all filesystems that have +ever had their checksum set to \fBskein\fR are destroyed. + +Booting off of pools using \fBskein\fR is supported. + +.RE + +.sp +.ne 2 +.na +\fB\fBbookmark_v2\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.datto:bookmark_v2 +READ\-ONLY COMPATIBLE no +DEPENDENCIES extensible_dataset +.TE + +This feature enables the creation and management of larger bookmarks which are +needed for other features in ZFS. + +This feature becomes \fBactive\fR when a v2 bookmark is created and will be +returned to the \fBenabled\fR state when all v2 bookmarks are destroyed. + +.RE + +.sp +.ne 2 +.na +\fB\fBedonr\fR\fR +.ad +.RS 4n +.TS +l l . +GUID org.illumos:edonr +READ\-ONLY COMPATIBLE no +DEPENDENCIES extensible_dataset +.TE + +This feature enables the use of the Edon-R hash algorithm for checksum, +including for nopwrite (if compression is also enabled, an overwrite of +a block whose checksum matches the data being written will be ignored). +In an abundance of caution, Edon-R can not be used with dedup +(without verification). + +Edon-R is a very high-performance hash algorithm that was part +of the NIST SHA-3 competition. It provides extremely high hash +performance (over 350% faster than SHA-256), but was not selected +because of its unsuitability as a general purpose secure hash algorithm. +This implementation utilizes the new salted checksumming functionality +in ZFS, which means that the checksum is pre-seeded with a secret +256-bit random key (stored on the pool) before being fed the data block +to be checksummed. Thus the produced checksums are unique to a given +pool. + +When the \fBedonr\fR feature is set to \fBenabled\fR, the administrator +can turn on the \fBedonr\fR checksum on any dataset using the +\fBzfs set checksum=edonr\fR command. This feature becomes +\fBactive\fR once a \fBchecksum\fR property has been set to \fBedonr\fR, +and will return to being \fBenabled\fR once all filesystems that have +ever had their checksum set to \fBedonr\fR are destroyed. + +Booting off of pools using \fBedonr\fR is supported. + +.RE + +.sp +.ne 2 +.na +\fB\fBallocation_classes\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.intel:allocation_classes +READ\-ONLY COMPATIBLE yes +DEPENDENCIES none +.TE + +This feature enables support for separate allocation classes. + +This feature becomes \fBactive\fR when a dedicated allocation class vdev +(dedup or special) is created with zpool create or zpool add. With device +removal, it can be returned to the \fBenabled\fR state if all the top-level +vdevs from an allocation class are removed. +.RE + +.sp +.ne 2 +.na +\fB\fBencryption\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.datto:encryption +READ\-ONLY COMPATIBLE no +DEPENDENCIES extensible_dataset +.TE + +This feature enables the creation and management of natively encrypted datasets. + +This feature becomes \fBactive\fR when an encrypted dataset is created +and will be returned to the \fBenabled\fR state when all datasets that +use this feature are destroyed. + +.RE +.sp +.ne 2 +.na +\fB\fBresilver_defer\fR\fR +.ad +.RS 4n +.TS +l l . +GUID com.datto:resilver_defer +READ\-ONLY COMPATIBLE yes +DEPENDENCIES none +.TE + +This feature allows zfs to postpone new resilvers if an existing one is already +in progress. Without this feature, any new resilvers will cause the currently +running one to be immediately restarted from the beginning. + +This feature becomes \fBactive\fR once a resilver has been deferred, and +returns to being \fBenabled\fR when the deferred resilver begins. +.RE + +.sp +.ne 2 +.na +\fBuserobj_accounting\fR +.ad +.RS 4n +.TS +l l . +GUID org.zfsonlinux:userobj_accounting +READ\-ONLY COMPATIBLE yes +DEPENDENCIES extensible_dataset +.TE + +This feature allows administrators to account the object usage information +by user and group. + +This feature becomes \fBactive\fR as soon as it is enabled and will never +return to being \fBenabled\fR. +Each filesystem will be upgraded automatically when remounted, or when new +files are created under that filesystem. +The upgrade can also be started manually on filesystems by running +`zfs set version=current <pool/fs>`. +The upgrade process runs in the background and may take a while to complete +for filesystems containing a large number of files. +.RE + +.sp +.ne 2 +.na +\fBproject_quota\fR +.ad +.RS 4n +.TS +l l . +GUID org.zfsonlinux:project_quota +READ\-ONLY COMPATIBLE yes +DEPENDENCIES extensible_dataset +.TE + +This feature allows administrators to account the space and object usage +information against the project identifier (ID). + +The project ID is a new object-based attribute. +When upgrading an existing filesystem, an object without a project ID +attribute will be assigned a zero project ID. +After this feature is enabled, a newly created object will inherit +its parent directory's project ID if the parent's inherit flag is set (via +\fBzfs project [-s|-C]\fR). +Otherwise, the new object's project ID will be set as zero. +An object's project ID can be changed at any time by the owner (or privileged +user) via \fBzfs project -p $prjid\fR. + +This feature will become \fBactive\fR as soon as it is enabled and will never +return to being \fBdisabled\fR. +Each filesystem will be upgraded automatically when remounted or when a new file +is created under that filesystem. +The upgrade can also be triggered on filesystems via `zfs set version=current +<pool/fs>`. +The upgrade process runs in the background and may take a while to complete +for the filesystems containing a large number of files. +.RE + +.sp +.ne 2 +.na +\fBlog_spacemap\fR +.ad +.RS 4n +.TS +l l . +GUID com.delphix:log_spacemap +READ\-ONLY COMPATIBLE yes +DEPENDENCIES com.delphix:spacemap_v2 +.TE + +This feature improves performance for heavily-fragmented pools, +especially when workloads are heavy in random-writes. +It does so by logging all the metaslab changes on a single spacemap every TXG +instead of scattering multiple writes to all the metaslab spacemaps. + +This feature becomes \fBactive\fR as soon as it is enabled and will never +return to being \fBenabled\fR. +.RE + +.SH "SEE ALSO" +.BR zfs (8), +.BR zpool (8) |