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17 .TH ZPOOL-FEATURES 5 "Jun 8, 2018"
19 zpool\-features \- ZFS pool feature descriptions
23 ZFS pool on\-disk format versions are specified via "features" which replace
24 the old on\-disk format numbers (the last supported on\-disk format number is
25 28). To enable a feature on a pool use the \fBupgrade\fR subcommand of the
26 \fBzpool\fR(8) command, or set the \fBfeature@\fR\fIfeature_name\fR property
30 The pool format does not affect file system version compatibility or the ability
31 to send file systems between pools.
34 Since most features can be enabled independently of each other the on\-disk
35 format of the pool is specified by the set of all features marked as
36 \fBactive\fR on the pool. If the pool was created by another software version
37 this set may include unsupported features.
38 .SS "Identifying features"
41 Every feature has a guid of the form \fIcom.example:feature_name\fR. The reverse
42 DNS name ensures that the feature's guid is unique across all ZFS
43 implementations. When unsupported features are encountered on a pool they will
44 be identified by their guids. Refer to the documentation for the ZFS
45 implementation that created the pool for information about those features.
48 Each supported feature also has a short name. By convention a feature's short
49 name is the portion of its guid which follows the ':' (e.g.
50 \fIcom.example:feature_name\fR would have the short name \fIfeature_name\fR),
51 however a feature's short name may differ across ZFS implementations if
52 following the convention would result in name conflicts.
56 Features can be in one of three states:
63 This feature's on\-disk format changes are in effect on the pool. Support for
64 this feature is required to import the pool in read\-write mode. If this
65 feature is not read-only compatible, support is also required to import the pool
66 in read\-only mode (see "Read\-only compatibility").
75 An administrator has marked this feature as enabled on the pool, but the
76 feature's on\-disk format changes have not been made yet. The pool can still be
77 imported by software that does not support this feature, but changes may be made
78 to the on\-disk format at any time which will move the feature to the
79 \fBactive\fR state. Some features may support returning to the \fBenabled\fR
80 state after becoming \fBactive\fR. See feature\-specific documentation for
90 This feature's on\-disk format changes have not been made and will not be made
91 unless an administrator moves the feature to the \fBenabled\fR state. Features
92 cannot be disabled once they have been enabled.
97 The state of supported features is exposed through pool properties of the form
98 \fIfeature@short_name\fR.
99 .SS "Read\-only compatibility"
102 Some features may make on\-disk format changes that do not interfere with other
103 software's ability to read from the pool. These features are referred to as
104 "read\-only compatible". If all unsupported features on a pool are read\-only
105 compatible, the pool can be imported in read\-only mode by setting the
106 \fBreadonly\fR property during import (see \fBzpool\fR(8) for details on
108 .SS "Unsupported features"
111 For each unsupported feature enabled on an imported pool a pool property
112 named \fIunsupported@feature_guid\fR will indicate why the import was allowed
113 despite the unsupported feature. Possible values for this property are:
121 The feature is in the \fBenabled\fR state and therefore the pool's on\-disk
122 format is still compatible with software that does not support this feature.
131 The feature is read\-only compatible and the pool has been imported in
135 .SS "Feature dependencies"
138 Some features depend on other features being enabled in order to function
139 properly. Enabling a feature will automatically enable any features it
144 The following features are supported on this system:
148 \fB\fBasync_destroy\fR\fR
153 GUID com.delphix:async_destroy
154 READ\-ONLY COMPATIBLE yes
158 Destroying a file system requires traversing all of its data in order to
159 return its used space to the pool. Without \fBasync_destroy\fR the file system
160 is not fully removed until all space has been reclaimed. If the destroy
161 operation is interrupted by a reboot or power outage the next attempt to open
162 the pool will need to complete the destroy operation synchronously.
164 When \fBasync_destroy\fR is enabled the file system's data will be reclaimed
165 by a background process, allowing the destroy operation to complete without
166 traversing the entire file system. The background process is able to resume
167 interrupted destroys after the pool has been opened, eliminating the need
168 to finish interrupted destroys as part of the open operation. The amount
169 of space remaining to be reclaimed by the background process is available
170 through the \fBfreeing\fR property.
172 This feature is only \fBactive\fR while \fBfreeing\fR is non\-zero.
178 \fB\fBempty_bpobj\fR\fR
183 GUID com.delphix:empty_bpobj
184 READ\-ONLY COMPATIBLE yes
188 This feature increases the performance of creating and using a large
189 number of snapshots of a single filesystem or volume, and also reduces
190 the disk space required.
192 When there are many snapshots, each snapshot uses many Block Pointer
193 Objects (bpobj's) to track blocks associated with that snapshot.
194 However, in common use cases, most of these bpobj's are empty. This
195 feature allows us to create each bpobj on-demand, thus eliminating the
198 This feature is \fBactive\fR while there are any filesystems, volumes,
199 or snapshots which were created after enabling this feature.
205 \fB\fBfilesystem_limits\fR\fR
210 GUID com.joyent:filesystem_limits
211 READ\-ONLY COMPATIBLE yes
212 DEPENDENCIES extensible_dataset
215 This feature enables filesystem and snapshot limits. These limits can be used
216 to control how many filesystems and/or snapshots can be created at the point in
217 the tree on which the limits are set.
219 This feature is \fBactive\fR once either of the limit properties has been
220 set on a dataset. Once activated the feature is never deactivated.
226 \fB\fBlz4_compress\fR\fR
231 GUID org.illumos:lz4_compress
232 READ\-ONLY COMPATIBLE no
236 \fBlz4\fR is a high-performance real-time compression algorithm that
237 features significantly faster compression and decompression as well as a
238 higher compression ratio than the older \fBlzjb\fR compression.
239 Typically, \fBlz4\fR compression is approximately 50% faster on
240 compressible data and 200% faster on incompressible data than
241 \fBlzjb\fR. It is also approximately 80% faster on decompression, while
242 giving approximately 10% better compression ratio.
244 When the \fBlz4_compress\fR feature is set to \fBenabled\fR, the
245 administrator can turn on \fBlz4\fR compression on any dataset on the
246 pool using the \fBzfs\fR(8) command. Please note that doing so will
247 immediately activate the \fBlz4_compress\fR feature on the underlying
248 pool using the \fBzfs\fR(1M) command. Also, all newly written metadata
249 will be compressed with \fBlz4\fR algorithm. Since this feature is not
250 read-only compatible, this operation will render the pool unimportable
251 on systems without support for the \fBlz4_compress\fR feature.
253 Booting off of \fBlz4\fR-compressed root pools is supported.
255 This feature becomes \fBactive\fR as soon as it is enabled and will
256 never return to being \fBenabled\fB.
262 \fB\fBspacemap_histogram\fR\fR
267 GUID com.delphix:spacemap_histogram
268 READ\-ONLY COMPATIBLE yes
272 This features allows ZFS to maintain more information about how free space
273 is organized within the pool. If this feature is \fBenabled\fR, ZFS will
274 set this feature to \fBactive\fR when a new space map object is created or
275 an existing space map is upgraded to the new format. Once the feature is
276 \fBactive\fR, it will remain in that state until the pool is destroyed.
283 \fB\fBmulti_vdev_crash_dump\fR\fR
288 GUID com.joyent:multi_vdev_crash_dump
289 READ\-ONLY COMPATIBLE no
293 This feature allows a dump device to be configured with a pool comprised
294 of multiple vdevs. Those vdevs may be arranged in any mirrored or raidz
297 When the \fBmulti_vdev_crash_dump\fR feature is set to \fBenabled\fR,
298 the administrator can use the \fBdumpadm\fR(1M) command to configure a
299 dump device on a pool comprised of multiple vdevs.
301 Under Linux this feature is registered for compatibility but not used.
302 New pools created under Linux will have the feature \fBenabled\fR but
303 will never transition to \fB\fBactive\fR. This functionality is not
304 required in order to support crash dumps under Linux. Existing pools
305 where this feature is \fB\fBactive\fR can be imported.
311 \fB\fBextensible_dataset\fR\fR
316 GUID com.delphix:extensible_dataset
317 READ\-ONLY COMPATIBLE no
321 This feature allows more flexible use of internal ZFS data structures,
322 and exists for other features to depend on.
324 This feature will be \fBactive\fR when the first dependent feature uses it,
325 and will be returned to the \fBenabled\fR state when all datasets that use
326 this feature are destroyed.
333 \fB\fBbookmarks\fR\fR
338 GUID com.delphix:bookmarks
339 READ\-ONLY COMPATIBLE yes
340 DEPENDENCIES extensible_dataset
343 This feature enables use of the \fBzfs bookmark\fR subcommand.
345 This feature is \fBactive\fR while any bookmarks exist in the pool.
346 All bookmarks in the pool can be listed by running
347 \fBzfs list -t bookmark -r \fIpoolname\fR\fR.
354 \fB\fBenabled_txg\fR\fR
359 GUID com.delphix:enabled_txg
360 READ\-ONLY COMPATIBLE yes
364 Once this feature is enabled ZFS records the transaction group number
365 in which new features are enabled. This has no user-visible impact,
366 but other features may depend on this feature.
368 This feature becomes \fBactive\fR as soon as it is enabled and will
369 never return to being \fBenabled\fB.
376 \fB\fBhole_birth\fR\fR
381 GUID com.delphix:hole_birth
382 READ\-ONLY COMPATIBLE no
383 DEPENDENCIES enabled_txg
386 This feature improves performance of incremental sends ("zfs send -i")
387 and receives for objects with many holes. The most common case of
388 hole-filled objects is zvols.
390 An incremental send stream from snapshot \fBA\fR to snapshot \fBB\fR
391 contains information about every block that changed between \fBA\fR and
392 \fBB\fR. Blocks which did not change between those snapshots can be
393 identified and omitted from the stream using a piece of metadata called
394 the 'block birth time', but birth times are not recorded for holes (blocks
395 filled only with zeroes). Since holes created after \fBA\fR cannot be
396 distinguished from holes created before \fBA\fR, information about every
397 hole in the entire filesystem or zvol is included in the send stream.
399 For workloads where holes are rare this is not a problem. However, when
400 incrementally replicating filesystems or zvols with many holes (for
401 example a zvol formatted with another filesystem) a lot of time will
402 be spent sending and receiving unnecessary information about holes that
403 already exist on the receiving side.
405 Once the \fBhole_birth\fR feature has been enabled the block birth times
406 of all new holes will be recorded. Incremental sends between snapshots
407 created after this feature is enabled will use this new metadata to avoid
408 sending information about holes that already exist on the receiving side.
410 This feature becomes \fBactive\fR as soon as it is enabled and will
411 never return to being \fBenabled\fB.
418 \fB\fBembedded_data\fR\fR
423 GUID com.delphix:embedded_data
424 READ\-ONLY COMPATIBLE no
428 This feature improves the performance and compression ratio of
429 highly-compressible blocks. Blocks whose contents can compress to 112 bytes
430 or smaller can take advantage of this feature.
432 When this feature is enabled, the contents of highly-compressible blocks are
433 stored in the block "pointer" itself (a misnomer in this case, as it contains
434 the compressed data, rather than a pointer to its location on disk). Thus
435 the space of the block (one sector, typically 512 bytes or 4KB) is saved,
436 and no additional i/o is needed to read and write the data block.
438 This feature becomes \fBactive\fR as soon as it is enabled and will
439 never return to being \fBenabled\fR.
445 \fB\fBdevice_removal\fR\fR
450 GUID com.delphix:device_removal
451 READ\-ONLY COMPATIBLE no
455 This feature enables the "zpool remove" subcommand to remove top-level
456 vdevs, evacuating them to reduce the total size of the pool.
458 This feature becomes \fBactive\fR when the "zpool remove" command is used
459 on a top-level vdev, and will never return to being \fBenabled\fR.
465 \fB\fBobsolete_counts\fR\fR
470 GUID com.delphix:obsolete_counts
471 READ\-ONLY COMPATIBLE yes
472 DEPENDENCIES device_removal
475 This feature is an enhancement of device_removal, which will over time
476 reduce the memory used to track removed devices. When indirect blocks
477 are freed or remapped, we note that their part of the indirect mapping
478 is "obsolete", i.e. no longer needed. See also the \fBzfs remap\fR
479 subcommand in \fBzfs\fR(1M).
481 This feature becomes \fBactive\fR when the "zpool remove" command is
482 used on a top-level vdev, and will never return to being \fBenabled\fR.
488 \fB\fBzpool_checkpoint\fR\fR
493 GUID com.delphix:zpool_checkpoint
494 READ\-ONLY COMPATIBLE yes
498 This feature enables the "zpool checkpoint" subcommand that can
499 checkpoint the state of the pool at the time it was issued and later
500 rewind back to it or discard it.
502 This feature becomes \fBactive\fR when the "zpool checkpoint" command
503 is used to checkpoint the pool.
504 The feature will only return back to being \fBenabled\fR when the pool
505 is rewound or the checkpoint has been discarded.
511 \fB\fBspacemap_v2\fR\fR
516 GUID com.delphix:spacemap_v2
517 READ\-ONLY COMPATIBLE yes
521 This feature enables the use of the new space map encoding which
522 consists of two words (instead of one) whenever it is advantageous.
523 The new encoding allows space maps to represent large regions of
524 space more efficiently on-disk while also increasing their maximum
527 This feature becomes \fBactive\fR once it is \fBenabled\fR, and never
528 returns back to being \fBenabled\fR.
534 \fB\fBlarge_blocks\fR\fR
539 GUID org.open-zfs:large_block
540 READ\-ONLY COMPATIBLE no
541 DEPENDENCIES extensible_dataset
544 The \fBlarge_block\fR feature allows the record size on a dataset to be
545 set larger than 128KB.
547 This feature becomes \fBactive\fR once a dataset contains a file with
548 a block size larger than 128KB, and will return to being \fBenabled\fR once all
549 filesystems that have ever had their recordsize larger than 128KB are destroyed.
555 \fB\fBlarge_dnode\fR\fR
560 GUID org.zfsonlinux:large_dnode
561 READ\-ONLY COMPATIBLE no
562 DEPENDENCIES extensible_dataset
565 The \fBlarge_dnode\fR feature allows the size of dnodes in a dataset to be
566 set larger than 512B.
568 This feature becomes \fBactive\fR once a dataset contains an object with
569 a dnode larger than 512B, which occurs as a result of setting the
570 \fBdnodesize\fR dataset property to a value other than \fBlegacy\fR. The
571 feature will return to being \fBenabled\fR once all filesystems that
572 have ever contained a dnode larger than 512B are destroyed. Large dnodes
573 allow more data to be stored in the bonus buffer, thus potentially
574 improving performance by avoiding the use of spill blocks.
582 GUID org.illumos:sha512
583 READ\-ONLY COMPATIBLE no
584 DEPENDENCIES extensible_dataset
587 This feature enables the use of the SHA-512/256 truncated hash algorithm
588 (FIPS 180-4) for checksum and dedup. The native 64-bit arithmetic of
589 SHA-512 provides an approximate 50% performance boost over SHA-256 on
590 64-bit hardware and is thus a good minimum-change replacement candidate
591 for systems where hash performance is important, but these systems
592 cannot for whatever reason utilize the faster \fBskein\fR and
593 \fBedonr\fR algorithms.
595 When the \fBsha512\fR feature is set to \fBenabled\fR, the administrator
596 can turn on the \fBsha512\fR checksum on any dataset using the
597 \fBzfs set checksum=sha512\fR(1M) command. This feature becomes
598 \fBactive\fR once a \fBchecksum\fR property has been set to \fBsha512\fR,
599 and will return to being \fBenabled\fR once all filesystems that have
600 ever had their checksum set to \fBsha512\fR are destroyed.
602 Booting off of pools utilizing SHA-512/256 is supported.
614 GUID org.illumos:skein
615 READ\-ONLY COMPATIBLE no
616 DEPENDENCIES extensible_dataset
619 This feature enables the use of the Skein hash algorithm for checksum
620 and dedup. Skein is a high-performance secure hash algorithm that was a
621 finalist in the NIST SHA-3 competition. It provides a very high security
622 margin and high performance on 64-bit hardware (80% faster than
623 SHA-256). This implementation also utilizes the new salted checksumming
624 functionality in ZFS, which means that the checksum is pre-seeded with a
625 secret 256-bit random key (stored on the pool) before being fed the data
626 block to be checksummed. Thus the produced checksums are unique to a
627 given pool, preventing hash collision attacks on systems with dedup.
629 When the \fBskein\fR feature is set to \fBenabled\fR, the administrator
630 can turn on the \fBskein\fR checksum on any dataset using the
631 \fBzfs set checksum=skein\fR(1M) command. This feature becomes
632 \fBactive\fR once a \fBchecksum\fR property has been set to \fBskein\fR,
633 and will return to being \fBenabled\fR once all filesystems that have
634 ever had their checksum set to \fBskein\fR are destroyed.
636 Booting off of pools using \fBskein\fR is supported.
648 GUID org.illumos:edonr
649 READ\-ONLY COMPATIBLE no
650 DEPENDENCIES extensible_dataset
653 This feature enables the use of the Edon-R hash algorithm for checksum,
654 including for nopwrite (if compression is also enabled, an overwrite of
655 a block whose checksum matches the data being written will be ignored).
656 In an abundance of caution, Edon-R can not be used with dedup
657 (without verification).
659 Edon-R is a very high-performance hash algorithm that was part
660 of the NIST SHA-3 competition. It provides extremely high hash
661 performance (over 350% faster than SHA-256), but was not selected
662 because of its unsuitability as a general purpose secure hash algorithm.
663 This implementation utilizes the new salted checksumming functionality
664 in ZFS, which means that the checksum is pre-seeded with a secret
665 256-bit random key (stored on the pool) before being fed the data block
666 to be checksummed. Thus the produced checksums are unique to a given
669 When the \fBedonr\fR feature is set to \fBenabled\fR, the administrator
670 can turn on the \fBedonr\fR checksum on any dataset using the
671 \fBzfs set checksum=edonr\fR(1M) command. This feature becomes
672 \fBactive\fR once a \fBchecksum\fR property has been set to \fBedonr\fR,
673 and will return to being \fBenabled\fR once all filesystems that have
674 ever had their checksum set to \fBedonr\fR are destroyed.
676 Booting off of pools using \fBedonr\fR is supported.
683 \fB\fBuserobj_accounting\fR\fR
688 GUID org.zfsonlinux:userobj_accounting
689 READ\-ONLY COMPATIBLE yes
690 DEPENDENCIES extensible_dataset
693 This feature allows administrators to account the object usage information
696 This feature becomes \fBactive\fR as soon as it is enabled and will never
697 return to being \fBenabled\fR. Each filesystem will be upgraded automatically
698 when remounted, or when new files are created under that filesystem.
699 The upgrade can also be started manually on filesystems by running
700 `zfs set version=current <pool/fs>`. The upgrade process runs in the background
701 and may take a while to complete for filesystems containing a large number of
709 \fB\fBencryption\fR\fR
714 GUID com.datto:encryption
715 READ\-ONLY COMPATIBLE no
716 DEPENDENCIES extensible_dataset
719 This feature enables the creation and management of natively encrypted datasets.
721 This feature becomes \fBactive\fR when an encrypted dataset is created and will
722 be returned to the \fBenabled\fR state when all datasets that use this feature
730 \fB\fBproject_quota\fR\fR
735 GUID org.zfsonlinux:project_quota
736 READ\-ONLY COMPATIBLE yes
737 DEPENDENCIES extensible_dataset
740 This feature allows administrators to account the spaces and objects usage
741 information against the project identifier (ID).
743 The project ID is new object-based attribute. When upgrading an existing
744 filesystem, object without project ID attribute will be assigned a zero
745 project ID. After this feature is enabled, newly created object will inherit
746 its parent directory's project ID if the parent inherit flag is set (via
747 \fBchattr +/-P\fR or \fBzfs project [-s|-C]\fR). Otherwise, the new object's
748 project ID will be set as zero. An object's project ID can be changed at
749 anytime by the owner (or privileged user) via \fBchattr -p $prjid\fR or
750 \fBzfs project -p $prjid\fR.
752 This feature will become \fBactive\fR as soon as it is enabled and will never
753 return to being \fBdisabled\fR. Each filesystem will be upgraded automatically
754 when remounted or when new file is created under that filesystem. The upgrade
755 can also be triggered on filesystems via `zfs set version=current <pool/fs>`.
756 The upgrade process runs in the background and may take a while to complete
757 for the filesystems containing a large number of files.
763 \fB\fBresilver_defer\fR\fR
768 GUID com.datto:resilver_defer
769 READ\-ONLY COMPATIBLE yes
773 This feature allows zfs to postpone new resilvers if an existing one is already
774 in progress. Without this feature, any new resilvers will cause the currently
775 running one to be immediately restarted from the beginning.
777 This feature becomes \fBactive\fR once a resilver has been defered, and returns
778 to being \fBenabled\fR when the defered resilver begins.
785 \fB\fBallocation_classes\fR\fR
790 GUID org.zfsonlinux:allocation_classes
791 READ\-ONLY COMPATIBLE yes
795 This feature enables support for separate allocation classes.
797 This feature becomes \fBactive\fR when a dedicated allocation class vdev
798 (dedup or special) is created with zpool create or zpool add. With device
799 removal, it can be returned to the \fBenabled\fR state if all the top-level
800 vdevs from an allocation class are removed.
projects / mirror_zfs.git / blob