xref: /freebsd/sys/contrib/openzfs/man/man7/zpool-features.7 (revision 3e8eb5c7f4909209c042403ddee340b2ee7003a5)
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21.Dd May 31, 2021
22.Dt ZPOOL-FEATURES 7
23.Os
24.
25.Sh NAME
26.Nm zpool-features
27.Nd description of ZFS pool features
28.
29.Sh DESCRIPTION
30ZFS pool on-disk format versions are specified via "features" which replace
31the old on-disk format numbers (the last supported on-disk format number is 28).
32To enable a feature on a pool use the
33.Nm zpool Cm upgrade ,
34or set the
35.Sy feature Ns @ Ns Ar feature-name
36property to
37.Sy enabled .
38Please also see the
39.Sx Compatibility feature sets
40section for information on how sets of features may be enabled together.
41.Pp
42The pool format does not affect file system version compatibility or the ability
43to send file systems between pools.
44.Pp
45Since most features can be enabled independently of each other, the on-disk
46format of the pool is specified by the set of all features marked as
47.Sy active
48on the pool.
49If the pool was created by another software version
50this set may include unsupported features.
51.
52.Ss Identifying features
53Every feature has a GUID of the form
54.Ar com.example : Ns Ar feature-name .
55The reversed DNS name ensures that the feature's GUID is unique across all ZFS
56implementations.
57When unsupported features are encountered on a pool they will
58be identified by their GUIDs.
59Refer to the documentation for the ZFS
60implementation that created the pool for information about those features.
61.Pp
62Each supported feature also has a short name.
63By convention a feature's short name is the portion of its GUID which follows the
64.Sq \&:
65(i.e.
66.Ar com.example : Ns Ar feature-name
67would have the short name
68.Ar feature-name ) ,
69however a feature's short name may differ across ZFS implementations if
70following the convention would result in name conflicts.
71.
72.Ss Feature states
73Features can be in one of three states:
74.Bl -tag -width "disabled"
75.It Sy active
76This feature's on-disk format changes are in effect on the pool.
77Support for this feature is required to import the pool in read-write mode.
78If this feature is not read-only compatible,
79support is also required to import the pool in read-only mode
80.Pq see Sx Read-only compatibility .
81.It Sy enabled
82An administrator has marked this feature as enabled on the pool, but the
83feature's on-disk format changes have not been made yet.
84The pool can still be imported by software that does not support this feature,
85but changes may be made to the on-disk format at any time
86which will move the feature to the
87.Sy active
88state.
89Some features may support returning to the
90.Sy enabled
91state after becoming
92.Sy active .
93See feature-specific documentation for details.
94.It Sy disabled
95This feature's on-disk format changes have not been made and will not be made
96unless an administrator moves the feature to the
97.Sy enabled
98state.
99Features cannot be disabled once they have been enabled.
100.El
101.Pp
102The state of supported features is exposed through pool properties of the form
103.Sy feature Ns @ Ns Ar short-name .
104.
105.Ss Read-only compatibility
106Some features may make on-disk format changes that do not interfere with other
107software's ability to read from the pool.
108These features are referred to as
109.Dq read-only compatible .
110If all unsupported features on a pool are read-only compatible,
111the pool can be imported in read-only mode by setting the
112.Sy readonly
113property during import (see
114.Xr zpool-import 8
115for details on importing pools).
116.
117.Ss Unsupported features
118For each unsupported feature enabled on an imported pool, a pool property
119named
120.Sy unsupported Ns @ Ns Ar feature-name
121will indicate why the import was allowed despite the unsupported feature.
122Possible values for this property are:
123.Bl -tag -width "readonly"
124.It Sy inactive
125The feature is in the
126.Sy enabled
127state and therefore the pool's on-disk
128format is still compatible with software that does not support this feature.
129.It Sy readonly
130The feature is read-only compatible and the pool has been imported in
131read-only mode.
132.El
133.
134.Ss Feature dependencies
135Some features depend on other features being enabled in order to function.
136Enabling a feature will automatically enable any features it depends on.
137.
138.Ss Compatibility feature sets
139It is sometimes necessary for a pool to maintain compatibility with a
140specific on-disk format, by enabling and disabling particular features.
141The
142.Sy compatibility
143feature facilitates this by allowing feature sets to be read from text files.
144When set to
145.Sy off
146(the default), compatibility feature sets are disabled
147(i.e. all features are enabled); when set to
148.Sy legacy ,
149no features are enabled.
150When set to a comma-separated list of filenames
151(each filename may either be an absolute path, or relative to
152.Pa /etc/zfs/compatibility.d
153or
154.Pa /usr/share/zfs/compatibility.d ) ,
155the lists of requested features are read from those files,
156separated by whitespace and/or commas.
157Only features present in all files are enabled.
158.Pp
159Simple sanity checks are applied to the files:
160they must be between 1 B and 16 KiB in size, and must end with a newline character.
161.Pp
162The requested features are applied when a pool is created using
163.Nm zpool Cm create Fl o Sy compatibility Ns = Ns Ar …
164and controls which features are enabled when using
165.Nm zpool Cm upgrade .
166.Nm zpool Cm status
167will not show a warning about disabled features which are not part
168of the requested feature set.
169.Pp
170The special value
171.Sy legacy
172prevents any features from being enabled, either via
173.Nm zpool Cm upgrade
174or
175.Nm zpool Cm set Sy feature Ns @ Ns Ar feature-name Ns = Ns Sy enabled .
176This setting also prevents pools from being upgraded to newer on-disk versions.
177This is a safety measure to prevent new features from being
178accidentally enabled, breaking compatibility.
179.Pp
180By convention, compatibility files in
181.Pa /usr/share/zfs/compatibility.d
182are provided by the distribution, and include feature sets
183supported by important versions of popular distributions, and feature
184sets commonly supported at the start of each year.
185Compatibility files in
186.Pa /etc/zfs/compatibility.d ,
187if present, will take precedence over files with the same name in
188.Pa /usr/share/zfs/compatibility.d .
189.Pp
190If an unrecognized feature is found in these files, an error message will
191be shown.
192If the unrecognized feature is in a file in
193.Pa /etc/zfs/compatibility.d ,
194this is treated as an error and processing will stop.
195If the unrecognized feature is under
196.Pa /usr/share/zfs/compatibility.d ,
197this is treated as a warning and processing will continue.
198This difference is to allow distributions to include features
199which might not be recognized by the currently-installed binaries.
200.Pp
201Compatibility files may include comments:
202any text from
203.Sq #
204to the end of the line is ignored.
205.Pp
206.Sy Example :
207.Bd -literal -compact -offset 4n
208.No example# Nm cat Pa /usr/share/zfs/compatibility.d/grub2
209# Features which are supported by GRUB2
210async_destroy
211bookmarks
212embedded_data
213empty_bpobj
214enabled_txg
215extensible_dataset
216filesystem_limits
217hole_birth
218large_blocks
219lz4_compress
220spacemap_histogram
221
222.No example# Nm zpool Cm create Fl o Sy compatibility Ns = Ns Ar grub2 Ar bootpool Ar vdev
223.Ed
224.Pp
225See
226.Xr zpool-create 8
227and
228.Xr zpool-upgrade 8
229for more information on how these commands are affected by feature sets.
230.
231.de feature
232.It Sy \\$2
233.Bl -tag -compact -width "READ-ONLY COMPATIBLE"
234.It GUID
235.Sy \\$1:\\$2
236.if !"\\$4"" \{\
237.It DEPENDENCIES
238\fB\\$4\fP\c
239.if !"\\$5"" , \fB\\$5\fP\c
240.if !"\\$6"" , \fB\\$6\fP\c
241.if !"\\$7"" , \fB\\$7\fP\c
242.if !"\\$8"" , \fB\\$8\fP\c
243.if !"\\$9"" , \fB\\$9\fP\c
244.\}
245.It READ-ONLY COMPATIBLE
246\\$3
247.El
248.Pp
249..
250.
251.ds instant-never \
252.No This feature becomes Sy active No as soon as it is enabled \
253and will never return to being Sy enabled .
254.
255.ds remount-upgrade \
256.No Each filesystem will be upgraded automatically when remounted, \
257or when a new file is created under that filesystem. \
258The upgrade can also be triggered on filesystems via \
259Nm zfs Cm set Sy version Ns = Ns Sy current Ar fs . \
260No The upgrade process runs in the background and may take a while to complete \
261for filesystems containing large amounts of files.
262.
263.de checksum-spiel
264When the
265.Sy \\$1
266feature is set to
267.Sy enabled ,
268the administrator can turn on the
269.Sy \\$1
270checksum on any dataset using
271.Nm zfs Cm set Sy checksum Ns = Ns Sy \\$1 Ar dset
272.Po see Xr zfs-set 8 Pc .
273This feature becomes
274.Sy active
275once a
276.Sy checksum
277property has been set to
278.Sy \\$1 ,
279and will return to being
280.Sy enabled
281once all filesystems that have ever had their checksum set to
282.Sy \\$1
283are destroyed.
284..
285.
286.Sh FEATURES
287The following features are supported on this system:
288.Bl -tag -width Ds
289.feature org.zfsonlinux allocation_classes yes
290This feature enables support for separate allocation classes.
291.Pp
292This feature becomes
293.Sy active
294when a dedicated allocation class vdev (dedup or special) is created with the
295.Nm zpool Cm create No or Nm zpool Cm add No commands .
296With device removal, it can be returned to the
297.Sy enabled
298state if all the dedicated allocation class vdevs are removed.
299.
300.feature com.delphix async_destroy yes
301Destroying a file system requires traversing all of its data in order to
302return its used space to the pool.
303Without
304.Sy async_destroy ,
305the file system is not fully removed until all space has been reclaimed.
306If the destroy operation is interrupted by a reboot or power outage,
307the next attempt to open the pool will need to complete the destroy
308operation synchronously.
309.Pp
310When
311.Sy async_destroy
312is enabled, the file system's data will be reclaimed by a background process,
313allowing the destroy operation to complete
314without traversing the entire file system.
315The background process is able to resume
316interrupted destroys after the pool has been opened, eliminating the need
317to finish interrupted destroys as part of the open operation.
318The amount of space remaining to be reclaimed by the background process
319is available through the
320.Sy freeing
321property.
322.Pp
323This feature is only
324.Sy active
325while
326.Sy freeing
327is non-zero.
328.
329.feature com.delphix bookmarks yes extensible_dataset
330This feature enables use of the
331.Nm zfs Cm bookmark
332command.
333.Pp
334This feature is
335.Sy active
336while any bookmarks exist in the pool.
337All bookmarks in the pool can be listed by running
338.Nm zfs Cm list Fl t Sy bookmark Fl r Ar poolname .
339.
340.feature com.datto bookmark_v2 no bookmark extensible_dataset
341This feature enables the creation and management of larger bookmarks which are
342needed for other features in ZFS.
343.Pp
344This feature becomes
345.Sy active
346when a v2 bookmark is created and will be returned to the
347.Sy enabled
348state when all v2 bookmarks are destroyed.
349.
350.feature com.delphix bookmark_written no bookmark extensible_dataset bookmark_v2
351This feature enables additional bookmark accounting fields, enabling the
352.Sy written Ns # Ns Ar bookmark
353property (space written since a bookmark) and estimates of
354send stream sizes for incrementals from bookmarks.
355.Pp
356This feature becomes
357.Sy active
358when a bookmark is created and will be
359returned to the
360.Sy enabled
361state when all bookmarks with these fields are destroyed.
362.
363.feature org.openzfs device_rebuild yes
364This feature enables the ability for the
365.Nm zpool Cm attach
366and
367.Nm zpool Cm replace
368commands to perform sequential reconstruction
369(instead of healing reconstruction) when resilvering.
370.Pp
371Sequential reconstruction resilvers a device in LBA order without immediately
372verifying the checksums.
373Once complete, a scrub is started, which then verifies the checksums.
374This approach allows full redundancy to be restored to the pool
375in the minimum amount of time.
376This two-phase approach will take longer than a healing resilver
377when the time to verify the checksums is included.
378However, unless there is additional pool damage,
379no checksum errors should be reported by the scrub.
380This feature is incompatible with raidz configurations.
381.
382This feature becomes
383.Sy active
384while a sequential resilver is in progress, and returns to
385.Sy enabled
386when the resilver completes.
387.
388.feature com.delphix device_removal no
389This feature enables the
390.Nm zpool Cm remove
391command to remove top-level vdevs,
392evacuating them to reduce the total size of the pool.
393.Pp
394This feature becomes
395.Sy active
396when the
397.Nm zpool Cm remove
398command is used
399on a top-level vdev, and will never return to being
400.Sy enabled .
401.
402.feature org.openzfs draid no
403This feature enables use of the
404.Sy draid
405vdev type.
406dRAID is a variant of RAID-Z which provides integrated distributed
407hot spares that allow faster resilvering while retaining the benefits of RAID-Z.
408Data, parity, and spare space are organized in redundancy groups
409and distributed evenly over all of the devices.
410.Pp
411This feature becomes
412.Sy active
413when creating a pool which uses the
414.Sy draid
415vdev type, or when adding a new
416.Sy draid
417vdev to an existing pool.
418.
419.feature org.illumos edonr no extensible_dataset
420This feature enables the use of the Edon-R hash algorithm for checksum,
421including for nopwrite (if compression is also enabled, an overwrite of
422a block whose checksum matches the data being written will be ignored).
423In an abundance of caution, Edon-R requires verification when used with
424dedup:
425.Nm zfs Cm set Sy dedup Ns = Ns Sy edonr , Ns Sy verify
426.Po see Xr zfs-set 8 Pc .
427.Pp
428Edon-R is a very high-performance hash algorithm that was part
429of the NIST SHA-3 competition.
430It provides extremely high hash performance (over 350% faster than SHA-256),
431but was not selected because of its unsuitability
432as a general purpose secure hash algorithm.
433This implementation utilizes the new salted checksumming functionality
434in ZFS, which means that the checksum is pre-seeded with a secret
435256-bit random key (stored on the pool) before being fed the data block
436to be checksummed.
437Thus the produced checksums are unique to a given pool,
438preventing hash collision attacks on systems with dedup.
439.
440.feature com.delphix embedded_data no
441This feature improves the performance and compression ratio of
442highly-compressible blocks.
443Blocks whose contents can compress to 112 bytes
444or smaller can take advantage of this feature.
445.Pp
446When this feature is enabled, the contents of highly-compressible blocks are
447stored in the block "pointer" itself (a misnomer in this case, as it contains
448the compressed data, rather than a pointer to its location on disk).
449Thus the space of the block (one sector, typically 512 B or 4 KiB) is saved,
450and no additional I/O is needed to read and write the data block.
451.
452\*[instant-never]
453.
454.feature com.delphix empty_bpobj yes
455This feature increases the performance of creating and using a large
456number of snapshots of a single filesystem or volume, and also reduces
457the disk space required.
458.Pp
459When there are many snapshots, each snapshot uses many Block Pointer
460Objects (bpobjs) to track blocks associated with that snapshot.
461However, in common use cases, most of these bpobjs are empty.
462This feature allows us to create each bpobj on-demand,
463thus eliminating the empty bpobjs.
464.Pp
465This feature is
466.Sy active
467while there are any filesystems, volumes,
468or snapshots which were created after enabling this feature.
469.
470.feature com.delphix enabled_txg yes
471Once this feature is enabled, ZFS records the transaction group number
472in which new features are enabled.
473This has no user-visible impact, but other features may depend on this feature.
474.Pp
475This feature becomes
476.Sy active
477as soon as it is enabled and will never return to being
478.Sy enabled .
479.
480.feature com.datto encryption no bookmark_v2 extensible_dataset
481This feature enables the creation and management of natively encrypted datasets.
482.Pp
483This feature becomes
484.Sy active
485when an encrypted dataset is created and will be returned to the
486.Sy enabled
487state when all datasets that use this feature are destroyed.
488.
489.feature com.delphix extensible_dataset no
490This feature allows more flexible use of internal ZFS data structures,
491and exists for other features to depend on.
492.Pp
493This feature will be
494.Sy active
495when the first dependent feature uses it, and will be returned to the
496.Sy enabled
497state when all datasets that use this feature are destroyed.
498.
499.feature com.joyent filesystem_limits yes extensible_dataset
500This feature enables filesystem and snapshot limits.
501These limits can be used to control how many filesystems and/or snapshots
502can be created at the point in the tree on which the limits are set.
503.Pp
504This feature is
505.Sy active
506once either of the limit properties has been set on a dataset
507and will never return to being
508.Sy enabled .
509.
510.feature com.delphix head_errlog no
511This feature enables the upgraded version of errlog, which required an on-disk
512error log format change.
513Now the error log of each head dataset is stored separately in the zap object
514and keyed by the head id.
515With this feature enabled, every dataset affected by an error block is listed
516in the output of
517.Nm zpool Cm status .
518.Pp
519\*[instant-never]
520.
521.feature com.delphix hole_birth no enabled_txg
522This feature has/had bugs, the result of which is that, if you do a
523.Nm zfs Cm send Fl i
524.Pq or Fl R , No since it uses Fl i
525from an affected dataset, the receiving party will not see any checksum
526or other errors, but the resulting destination snapshot
527will not match the source.
528Its use by
529.Nm zfs Cm send Fl i
530has been disabled by default
531.Pq see Sy send_holes_without_birth_time No in Xr zfs 4 .
532.Pp
533This feature improves performance of incremental sends
534.Pq Nm zfs Cm send Fl i
535and receives for objects with many holes.
536The most common case of hole-filled objects is zvols.
537.Pp
538An incremental send stream from snapshot
539.Sy A No to snapshot Sy B
540contains information about every block that changed between
541.Sy A No and Sy B .
542Blocks which did not change between those snapshots can be
543identified and omitted from the stream using a piece of metadata called
544the "block birth time", but birth times are not recorded for holes
545(blocks filled only with zeroes).
546Since holes created after
547.Sy A No cannot be distinguished from holes created before Sy A ,
548information about every hole in the entire filesystem or zvol
549is included in the send stream.
550.Pp
551For workloads where holes are rare this is not a problem.
552However, when incrementally replicating filesystems or zvols with many holes
553(for example a zvol formatted with another filesystem) a lot of time will
554be spent sending and receiving unnecessary information about holes that
555already exist on the receiving side.
556.Pp
557Once the
558.Sy hole_birth
559feature has been enabled the block birth times
560of all new holes will be recorded.
561Incremental sends between snapshots created after this feature is enabled
562will use this new metadata to avoid sending information about holes that
563already exist on the receiving side.
564.Pp
565\*[instant-never]
566.
567.feature org.open-zfs large_blocks no extensible_dataset
568This feature allows the record size on a dataset to be set larger than 128 KiB.
569.Pp
570This feature becomes
571.Sy active
572once a dataset contains a file with a block size larger than 128 KiB,
573and will return to being
574.Sy enabled
575once all filesystems that have ever had their recordsize larger than 128 KiB
576are destroyed.
577.
578.feature org.zfsonlinux large_dnode no extensible_dataset
579This feature allows the size of dnodes in a dataset to be set larger than 512 B.
580.
581This feature becomes
582.Sy active
583once a dataset contains an object with a dnode larger than 512 B,
584which occurs as a result of setting the
585.Sy dnodesize
586dataset property to a value other than
587.Sy legacy .
588The feature will return to being
589.Sy enabled
590once all filesystems that have ever contained a dnode larger than 512 B
591are destroyed.
592Large dnodes allow more data to be stored in the bonus buffer,
593thus potentially improving performance by avoiding the use of spill blocks.
594.
595.feature com.delphix livelist yes
596This feature allows clones to be deleted faster than the traditional method
597when a large number of random/sparse writes have been made to the clone.
598All blocks allocated and freed after a clone is created are tracked by the
599the clone's livelist which is referenced during the deletion of the clone.
600The feature is activated when a clone is created and remains
601.Sy active
602until all clones have been destroyed.
603.
604.feature com.delphix log_spacemap yes com.delphix:spacemap_v2
605This feature improves performance for heavily-fragmented pools,
606especially when workloads are heavy in random-writes.
607It does so by logging all the metaslab changes on a single spacemap every TXG
608instead of scattering multiple writes to all the metaslab spacemaps.
609.Pp
610\*[instant-never]
611.
612.feature org.illumos lz4_compress no
613.Sy lz4
614is a high-performance real-time compression algorithm that
615features significantly faster compression and decompression as well as a
616higher compression ratio than the older
617.Sy lzjb
618compression.
619Typically,
620.Sy lz4
621compression is approximately 50% faster on compressible data and 200% faster
622on incompressible data than
623.Sy lzjb .
624It is also approximately 80% faster on decompression,
625while giving approximately a 10% better compression ratio.
626.Pp
627When the
628.Sy lz4_compress
629feature is set to
630.Sy enabled ,
631the administrator can turn on
632.Sy lz4
633compression on any dataset on the pool using the
634.Xr zfs-set 8
635command.
636All newly written metadata will be compressed with the
637.Sy lz4
638algorithm.
639.Pp
640\*[instant-never]
641.
642.feature com.joyent multi_vdev_crash_dump no
643This feature allows a dump device to be configured with a pool comprised
644of multiple vdevs.
645Those vdevs may be arranged in any mirrored or raidz configuration.
646.Pp
647When the
648.Sy multi_vdev_crash_dump
649feature is set to
650.Sy enabled ,
651the administrator can use
652.Xr dumpadm 1M
653to configure a dump device on a pool comprised of multiple vdevs.
654.Pp
655Under
656.Fx
657and Linux this feature is unused, but registered for compatibility.
658New pools created on these systems will have the feature
659.Sy enabled
660but will never transition to
661.Sy active ,
662as this functionality is not required for crash dump support.
663Existing pools where this feature is
664.Sy active
665can be imported.
666.
667.feature com.delphix obsolete_counts yes device_removal
668This feature is an enhancement of
669.Sy device_removal ,
670which will over time reduce the memory used to track removed devices.
671When indirect blocks are freed or remapped,
672we note that their part of the indirect mapping is "obsolete" – no longer needed.
673.Pp
674This feature becomes
675.Sy active
676when the
677.Nm zpool Cm remove
678command is used on a top-level vdev, and will never return to being
679.Sy enabled .
680.
681.feature org.zfsonlinux project_quota yes extensible_dataset
682This feature allows administrators to account the spaces and objects usage
683information against the project identifier (ID).
684.Pp
685The project ID is an object-based attribute.
686When upgrading an existing filesystem,
687objects without a project ID will be assigned a zero project ID.
688When this feature is enabled, newly created objects inherit
689their parent directories' project ID if the parent's inherit flag is set
690.Pq via Nm chattr Sy [+-]P No or Nm zfs Cm project Fl s Ns | Ns Fl C .
691Otherwise, the new object's project ID will be zero.
692An object's project ID can be changed at any time by the owner
693(or privileged user) via
694.Nm chattr Fl p Ar prjid
695or
696.Nm zfs Cm project Fl p Ar prjid .
697.Pp
698This feature will become
699.Sy active
700as soon as it is enabled and will never return to being
701.Sy disabled .
702\*[remount-upgrade]
703.
704.feature com.delphix redaction_bookmarks no bookmarks extensible_dataset
705This feature enables the use of redacted
706.Nm zfs Cm send Ns s ,
707which create redaction bookmarks storing the list of blocks
708redacted by the send that created them.
709For more information about redacted sends, see
710.Xr zfs-send 8 .
711.
712.feature com.delphix redacted_datasets no extensible_dataset
713This feature enables the receiving of redacted
714.Nm zfs Cm send
715streams, which create redacted datasets when received.
716These datasets are missing some of their blocks,
717and so cannot be safely mounted, and their contents cannot be safely read.
718For more information about redacted receives, see
719.Xr zfs-send 8 .
720.
721.feature com.datto resilver_defer yes
722This feature allows ZFS to postpone new resilvers if an existing one is already
723in progress.
724Without this feature, any new resilvers will cause the currently
725running one to be immediately restarted from the beginning.
726.Pp
727This feature becomes
728.Sy active
729once a resilver has been deferred, and returns to being
730.Sy enabled
731when the deferred resilver begins.
732.
733.feature org.illumos sha512 no extensible_dataset
734This feature enables the use of the SHA-512/256 truncated hash algorithm
735(FIPS 180-4) for checksum and dedup.
736The native 64-bit arithmetic of SHA-512 provides an approximate 50%
737performance boost over SHA-256 on 64-bit hardware
738and is thus a good minimum-change replacement candidate
739for systems where hash performance is important,
740but these systems cannot for whatever reason utilize the faster
741.Sy skein No and Sy edonr
742algorithms.
743.Pp
744.checksum-spiel sha512
745.
746.feature org.illumos skein no extensible_dataset
747This feature enables the use of the Skein hash algorithm for checksum and dedup.
748Skein is a high-performance secure hash algorithm that was a
749finalist in the NIST SHA-3 competition.
750It provides a very high security margin and high performance on 64-bit hardware
751(80% faster than SHA-256).
752This implementation also utilizes the new salted checksumming
753functionality in ZFS, which means that the checksum is pre-seeded with a
754secret 256-bit random key (stored on the pool) before being fed the data
755block to be checksummed.
756Thus the produced checksums are unique to a given pool,
757preventing hash collision attacks on systems with dedup.
758.Pp
759.checksum-spiel skein
760.
761.feature com.delphix spacemap_histogram yes
762This features allows ZFS to maintain more information about how free space
763is organized within the pool.
764If this feature is
765.Sy enabled ,
766it will be activated when a new space map object is created, or
767an existing space map is upgraded to the new format,
768and never returns back to being
769.Sy enabled .
770.
771.feature com.delphix spacemap_v2 yes
772This feature enables the use of the new space map encoding which
773consists of two words (instead of one) whenever it is advantageous.
774The new encoding allows space maps to represent large regions of
775space more efficiently on-disk while also increasing their maximum
776addressable offset.
777.Pp
778This feature becomes
779.Sy active
780once it is
781.Sy enabled ,
782and never returns back to being
783.Sy enabled .
784.
785.feature org.zfsonlinux userobj_accounting yes extensible_dataset
786This feature allows administrators to account the object usage information
787by user and group.
788.Pp
789\*[instant-never]
790\*[remount-upgrade]
791.
792.feature org.openzfs zilsaxattr yes extensible_dataset
793This feature enables
794.Sy xattr Ns = Ns Sy sa
795extended attribute logging in the ZIL.
796If enabled, extended attribute changes
797.Pq both Sy xattrdir Ns = Ns Sy dir No and Sy xattr Ns = Ns Sy sa
798are guaranteed to be durable if either the dataset had
799.Sy sync Ns = Ns Sy always
800set at the time the changes were made, or
801.Xr sync 2
802is called on the dataset after the changes were made.
803.Pp
804This feature becomes
805.Sy active
806when a ZIL is created for at least one dataset and will be returned to the
807.Sy enabled
808state when it is destroyed for all datasets that use this feature.
809.
810.feature com.delphix zpool_checkpoint yes
811This feature enables the
812.Nm zpool Cm checkpoint
813command that can checkpoint the state of the pool
814at the time it was issued and later rewind back to it or discard it.
815.Pp
816This feature becomes
817.Sy active
818when the
819.Nm zpool Cm checkpoint
820command is used to checkpoint the pool.
821The feature will only return back to being
822.Sy enabled
823when the pool is rewound or the checkpoint has been discarded.
824.
825.feature org.freebsd zstd_compress no extensible_dataset
826.Sy zstd
827is a high-performance compression algorithm that features a
828combination of high compression ratios and high speed.
829Compared to
830.Sy gzip ,
831.Sy zstd
832offers slightly better compression at much higher speeds.
833Compared to
834.Sy lz4 ,
835.Sy zstd
836offers much better compression while being only modestly slower.
837Typically,
838.Sy zstd
839compression speed ranges from 250 to 500 MB/s per thread
840and decompression speed is over 1 GB/s per thread.
841.Pp
842When the
843.Sy zstd
844feature is set to
845.Sy enabled ,
846the administrator can turn on
847.Sy zstd
848compression of any dataset using
849.Nm zfs Cm set Sy compress Ns = Ns Sy zstd Ar dset
850.Po see Xr zfs-set 8 Pc .
851This feature becomes
852.Sy active
853once a
854.Sy compress
855property has been set to
856.Sy zstd ,
857and will return to being
858.Sy enabled
859once all filesystems that have ever had their
860.Sy compress
861property set to
862.Sy zstd
863are destroyed.
864.El
865.
866.Sh SEE ALSO
867.Xr zpool 8
868