2 .\" Copyright (c) 2013, 2017 by Delphix. All rights reserved.
3 .\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
4 .\" Copyright (c) 2014, Joyent, Inc. All rights reserved.
5 .\" The contents of this file are subject to the terms of the Common Development
6 .\" and Distribution License (the "License"). You may not use this file except
7 .\" in compliance with the License. You can obtain a copy of the license at
8 .\" usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.
10 .\" See the License for the specific language governing permissions and
11 .\" limitations under the License. When distributing Covered Code, include this
12 .\" CDDL HEADER in each file and include the License file at
13 .\" usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this
14 .\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your
15 .\" own identifying information:
16 .\" Portions Copyright [yyyy] [name of copyright owner]
17 .TH ZPOOL-FEATURES 5 "Aug 27, 2013"
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. Booting
252 off of \fBlz4\fR-compressed root pools is supported.
254 This feature becomes \fBactive\fR as soon as it is enabled and will
255 never return to being \fBenabled\fB.
261 \fB\fBspacemap_histogram\fR\fR
266 GUID com.delphix:spacemap_histogram
267 READ\-ONLY COMPATIBLE yes
271 This features allows ZFS to maintain more information about how free space
272 is organized within the pool. If this feature is \fBenabled\fR, ZFS will
273 set this feature to \fBactive\fR when a new space map object is created or
274 an existing space map is upgraded to the new format. Once the feature is
275 \fBactive\fR, it will remain in that state until the pool is destroyed.
282 \fB\fBmulti_vdev_crash_dump\fR\fR
287 GUID com.joyent:multi_vdev_crash_dump
288 READ\-ONLY COMPATIBLE no
292 This feature allows a dump device to be configured with a pool comprised
293 of multiple vdevs. Those vdevs may be arranged in any mirrored or raidz
296 When the \fBmulti_vdev_crash_dump\fR feature is set to \fBenabled\fR,
297 the administrator can use the \fBdumpadm\fR(1M) command to configure a
298 dump device on a pool comprised of multiple vdevs.
300 Under Linux this feature is registered for compatibility but not used.
301 New pools created under Linux will have the feature \fBenabled\fR but
302 will never transition to \fB\fBactive\fR. This functionality is not
303 required in order to support crash dumps under Linux. Existing pools
304 where this feature is \fB\fBactive\fR can be imported.
310 \fB\fBextensible_dataset\fR\fR
315 GUID com.delphix:extensible_dataset
316 READ\-ONLY COMPATIBLE no
320 This feature allows more flexible use of internal ZFS data structures,
321 and exists for other features to depend on.
323 This feature will be \fBactive\fR when the first dependent feature uses it,
324 and will be returned to the \fBenabled\fR state when all datasets that use
325 this feature are destroyed.
332 \fB\fBbookmarks\fR\fR
337 GUID com.delphix:bookmarks
338 READ\-ONLY COMPATIBLE yes
339 DEPENDENCIES extensible_dataset
342 This feature enables use of the \fBzfs bookmark\fR subcommand.
344 This feature is \fBactive\fR while any bookmarks exist in the pool.
345 All bookmarks in the pool can be listed by running
346 \fBzfs list -t bookmark -r \fIpoolname\fR\fR.
353 \fB\fBenabled_txg\fR\fR
358 GUID com.delphix:enabled_txg
359 READ\-ONLY COMPATIBLE yes
363 Once this feature is enabled ZFS records the transaction group number
364 in which new features are enabled. This has no user-visible impact,
365 but other features may depend on this feature.
367 This feature becomes \fBactive\fR as soon as it is enabled and will
368 never return to being \fBenabled\fB.
375 \fB\fBhole_birth\fR\fR
380 GUID com.delphix:hole_birth
381 READ\-ONLY COMPATIBLE no
382 DEPENDENCIES enabled_txg
385 This feature improves performance of incremental sends ("zfs send -i")
386 and receives for objects with many holes. The most common case of
387 hole-filled objects is zvols.
389 An incremental send stream from snapshot \fBA\fR to snapshot \fBB\fR
390 contains information about every block that changed between \fBA\fR and
391 \fBB\fR. Blocks which did not change between those snapshots can be
392 identified and omitted from the stream using a piece of metadata called
393 the 'block birth time', but birth times are not recorded for holes (blocks
394 filled only with zeroes). Since holes created after \fBA\fR cannot be
395 distinguished from holes created before \fBA\fR, information about every
396 hole in the entire filesystem or zvol is included in the send stream.
398 For workloads where holes are rare this is not a problem. However, when
399 incrementally replicating filesystems or zvols with many holes (for
400 example a zvol formatted with another filesystem) a lot of time will
401 be spent sending and receiving unnecessary information about holes that
402 already exist on the receiving side.
404 Once the \fBhole_birth\fR feature has been enabled the block birth times
405 of all new holes will be recorded. Incremental sends between snapshots
406 created after this feature is enabled will use this new metadata to avoid
407 sending information about holes that already exist on the receiving side.
409 This feature becomes \fBactive\fR as soon as it is enabled and will
410 never return to being \fBenabled\fB.
417 \fB\fBembedded_data\fR\fR
422 GUID com.delphix:embedded_data
423 READ\-ONLY COMPATIBLE no
427 This feature improves the performance and compression ratio of
428 highly-compressible blocks. Blocks whose contents can compress to 112 bytes
429 or smaller can take advantage of this feature.
431 When this feature is enabled, the contents of highly-compressible blocks are
432 stored in the block "pointer" itself (a misnomer in this case, as it contains
433 the compressed data, rather than a pointer to its location on disk). Thus
434 the space of the block (one sector, typically 512 bytes or 4KB) is saved,
435 and no additional i/o is needed to read and write the data block.
437 This feature becomes \fBactive\fR as soon as it is enabled and will
438 never return to being \fBenabled\fR.
444 \fB\fBdevice_removal\fR\fR
449 GUID com.delphix:device_removal
450 READ\-ONLY COMPATIBLE no
454 This feature enables the "zpool remove" subcommand to remove top-level
455 vdevs, evacuating them to reduce the total size of the pool.
457 This feature becomes \fBactive\fR when the "zpool remove" command is used
458 on a top-level vdev, and will never return to being \fBenabled\fR.
464 \fB\fBobsolete_counts\fR\fR
469 GUID com.delphix:obsolete_counts
470 READ\-ONLY COMPATIBLE yes
471 DEPENDENCIES device_removal
474 This feature is an enhancement of device_removal, which will over time
475 reduce the memory used to track removed devices. When indirect blocks
476 are freed or remapped, we note that their part of the indirect mapping
477 is "obsolete", i.e. no longer needed. See also the \fBzfs remap\fR
478 subcommand in \fBzfs\fR(1M).
480 This feature becomes \fBactive\fR when the "zpool remove" command is
481 used on a top-level vdev, and will never return to being \fBenabled\fR.
487 \fB\fBzpool_checkpoint\fR\fR
492 GUID com.delphix:zpool_checkpoint
493 READ\-ONLY COMPATIBLE yes
497 This feature enables the "zpool checkpoint" subcommand that can
498 checkpoint the state of the pool at the time it was issued and later
499 rewind back to it or discard it.
501 This feature becomes \fBactive\fR when the "zpool checkpoint" command
502 is used to checkpoint the pool.
503 The feature will only return back to being \fBenabled\fR when the pool
504 is rewound or the checkpoint has been discarded.
505 \fB\fBlarge_blocks\fR\fR
510 GUID org.open-zfs:large_block
511 READ\-ONLY COMPATIBLE no
512 DEPENDENCIES extensible_dataset
515 The \fBlarge_block\fR feature allows the record size on a dataset to be
516 set larger than 128KB.
518 This feature becomes \fBactive\fR once a dataset contains a file with
519 a block size larger than 128KB, and will return to being \fBenabled\fR once all
520 filesystems that have ever had their recordsize larger than 128KB are destroyed.
526 \fB\fBlarge_dnode\fR\fR
531 GUID org.zfsonlinux:large_dnode
532 READ\-ONLY COMPATIBLE no
533 DEPENDENCIES extensible_dataset
536 The \fBlarge_dnode\fR feature allows the size of dnodes in a dataset to be
537 set larger than 512B.
539 This feature becomes \fBactive\fR once a dataset contains an object with
540 a dnode larger than 512B, which occurs as a result of setting the
541 \fBdnodesize\fR dataset property to a value other than \fBlegacy\fR. The
542 feature will return to being \fBenabled\fR once all filesystems that
543 have ever contained a dnode larger than 512B are destroyed. Large dnodes
544 allow more data to be stored in the bonus buffer, thus potentially
545 improving performance by avoiding the use of spill blocks.
553 GUID org.illumos:sha512
554 READ\-ONLY COMPATIBLE no
555 DEPENDENCIES extensible_dataset
558 This feature enables the use of the SHA-512/256 truncated hash algorithm
559 (FIPS 180-4) for checksum and dedup. The native 64-bit arithmetic of
560 SHA-512 provides an approximate 50% performance boost over SHA-256 on
561 64-bit hardware and is thus a good minimum-change replacement candidate
562 for systems where hash performance is important, but these systems
563 cannot for whatever reason utilize the faster \fBskein\fR and
564 \fBedonr\fR algorithms.
566 When the \fBsha512\fR feature is set to \fBenabled\fR, the administrator
567 can turn on the \fBsha512\fR checksum on any dataset using the
568 \fBzfs set checksum=sha512\fR(1M) command. This feature becomes
569 \fBactive\fR once a \fBchecksum\fR property has been set to \fBsha512\fR,
570 and will return to being \fBenabled\fR once all filesystems that have
571 ever had their checksum set to \fBsha512\fR are destroyed.
573 Booting off of pools utilizing SHA-512/256 is supported (provided that
574 the updated GRUB stage2 module is installed).
586 GUID org.illumos:skein
587 READ\-ONLY COMPATIBLE no
588 DEPENDENCIES extensible_dataset
591 This feature enables the use of the Skein hash algorithm for checksum
592 and dedup. Skein is a high-performance secure hash algorithm that was a
593 finalist in the NIST SHA-3 competition. It provides a very high security
594 margin and high performance on 64-bit hardware (80% faster than
595 SHA-256). This implementation also utilizes the new salted checksumming
596 functionality in ZFS, which means that the checksum is pre-seeded with a
597 secret 256-bit random key (stored on the pool) before being fed the data
598 block to be checksummed. Thus the produced checksums are unique to a
599 given pool, preventing hash collision attacks on systems with dedup.
601 When the \fBskein\fR feature is set to \fBenabled\fR, the administrator
602 can turn on the \fBskein\fR checksum on any dataset using the
603 \fBzfs set checksum=skein\fR(1M) command. This feature becomes
604 \fBactive\fR once a \fBchecksum\fR property has been set to \fBskein\fR,
605 and will return to being \fBenabled\fR once all filesystems that have
606 ever had their checksum set to \fBskein\fR are destroyed.
608 Booting off of pools using \fBskein\fR is \fBNOT\fR supported
609 -- any attempt to enable \fBskein\fR on a root pool will fail with an
622 GUID org.illumos:edonr
623 READ\-ONLY COMPATIBLE no
624 DEPENDENCIES extensible_dataset
627 This feature enables the use of the Edon-R hash algorithm for checksum,
628 including for nopwrite (if compression is also enabled, an overwrite of
629 a block whose checksum matches the data being written will be ignored).
630 In an abundance of caution, Edon-R can not be used with dedup
631 (without verification).
633 Edon-R is a very high-performance hash algorithm that was part
634 of the NIST SHA-3 competition. It provides extremely high hash
635 performance (over 350% faster than SHA-256), but was not selected
636 because of its unsuitability as a general purpose secure hash algorithm.
637 This implementation utilizes the new salted checksumming functionality
638 in ZFS, which means that the checksum is pre-seeded with a secret
639 256-bit random key (stored on the pool) before being fed the data block
640 to be checksummed. Thus the produced checksums are unique to a given
643 When the \fBedonr\fR feature is set to \fBenabled\fR, the administrator
644 can turn on the \fBedonr\fR checksum on any dataset using the
645 \fBzfs set checksum=edonr\fR(1M) command. This feature becomes
646 \fBactive\fR once a \fBchecksum\fR property has been set to \fBedonr\fR,
647 and will return to being \fBenabled\fR once all filesystems that have
648 ever had their checksum set to \fBedonr\fR are destroyed.
650 Booting off of pools using \fBedonr\fR is \fBNOT\fR supported
651 -- any attempt to enable \fBedonr\fR on a root pool will fail with an
659 \fB\fBuserobj_accounting\fR\fR
664 GUID org.zfsonlinux:userobj_accounting
665 READ\-ONLY COMPATIBLE yes
666 DEPENDENCIES extensible_dataset
669 This feature allows administrators to account the object usage information
672 This feature becomes \fBactive\fR as soon as it is enabled and will never
673 return to being \fBenabled\fR. Each filesystem will be upgraded automatically
674 when remounted, or when new files are created under that filesystem.
675 The upgrade can also be started manually on filesystems by running
676 `zfs set version=current <pool/fs>`. The upgrade process runs in the background
677 and may take a while to complete for filesystems containing a large number of
685 \fB\fBencryption\fR\fR
690 GUID com.datto:encryption
691 READ\-ONLY COMPATIBLE no
692 DEPENDENCIES extensible_dataset
695 This feature enables the creation and management of natively encrypted datasets.
697 This feature becomes \fBactive\fR when an encrypted dataset is created and will
698 be returned to the \fBenabled\fR state when all datasets that use this feature
706 \fB\fBproject_quota\fR\fR
711 GUID org.zfsonlinux:project_quota
712 READ\-ONLY COMPATIBLE yes
713 DEPENDENCIES extensible_dataset
716 This feature allows administrators to account the spaces and objects usage
717 information against the project identifier (ID).
719 The project ID is new object-based attribute. When upgrading an existing
720 filesystem, object without project ID attribute will be assigned a zero
721 project ID. After this feature is enabled, newly created object will inherit
722 its parent directory's project ID if the parent inherit flag is set (via
723 \fBchattr +/-P\fR or \fBzfs project [-s|-C]\fR). Otherwise, the new object's
724 project ID will be set as zero. An object's project ID can be changed at
725 anytime by the owner (or privileged user) via \fBchattr -p $prjid\fR or
726 \fBzfs project -p $prjid\fR.
728 This feature will become \fBactive\fR as soon as it is enabled and will never
729 return to being \fBdisabled\fR. Each filesystem will be upgraded automatically
730 when remounted or when new file is created under that filesystem. The upgrade
731 can also be triggered on filesystems via `zfs set version=current <pool/fs>`.
732 The upgrade process runs in the background and may take a while to complete
733 for the filesystems containing a large number of files.
projects / mirror_zfs.git / blob