1'\" te 2.\" Copyright (c) 2012, Martin Matuska <mm@FreeBSD.org>. 3.\" All Rights Reserved. 4.\" 5.\" The contents of this file are subject to the terms of the 6.\" Common Development and Distribution License (the "License"). 7.\" You may not use this file except in compliance with the License. 8.\" 9.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 10.\" or http://www.opensolaris.org/os/licensing. 11.\" See the License for the specific language governing permissions 12.\" and limitations under the License. 13.\" 14.\" When distributing Covered Code, include this CDDL HEADER in each 15.\" file and include the License file at usr/src/OPENSOLARIS.LICENSE. 16.\" If applicable, add the following below this CDDL HEADER, with the 17.\" fields enclosed by brackets "[]" replaced with your own identifying 18.\" information: Portions Copyright [yyyy] [name of copyright owner] 19.\" 20.\" Copyright (c) 2012 by Delphix. All rights reserved. 21.\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved. 22.\" Copyright (c) 2013, Joyent, Inc. All rights reserved. 23.\" 24.\" $FreeBSD: head/cddl/contrib/opensolaris/cmd/zpool/zpool-features.7 301104 2016-06-01 06:18:34Z allanjude $ 25.\" 26.Dd May 31, 2016 27.Dt ZPOOL-FEATURES 7 28.Os 29.Sh NAME 30.Nm zpool-features 31.Nd ZFS pool feature descriptions 32.Sh DESCRIPTION 33ZFS pool on\-disk format versions are specified via "features" which replace 34the old on\-disk format numbers (the last supported on\-disk format number is 3528). 36To enable a feature on a pool use the 37.Cm upgrade 38subcommand of the 39.Xr zpool 8 40command, or set the 41.Sy feature@feature_name 42property to 43.Ar enabled . 44.Pp 45The pool format does not affect file system version compatibility or the ability 46to send file systems between pools. 47.Pp 48Since most features can be enabled independently of each other the on\-disk 49format of the pool is specified by the set of all features marked as 50.Sy active 51on the pool. If the pool was created by another software version this set may 52include unsupported features. 53.Ss Identifying features 54Every feature has a guid of the form 55.Sy com.example:feature_name . 56The reverse DNS name ensures that the feature's guid is unique across all ZFS 57implementations. When unsupported features are encountered on a pool they will 58be identified by their guids. 59Refer to the documentation for the ZFS implementation that created the pool 60for 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 64the ':' (e.g. 65.Sy com.example:feature_name 66would have the short name 67.Sy feature_name ), 68however a feature's short name may differ across ZFS implementations if 69following the convention would result in name conflicts. 70.Ss Feature states 71Features can be in one of three states: 72.Bl -tag -width "XXXXXXXX" 73.It Sy active 74This feature's on\-disk format changes are in effect on the pool. 75Support for this feature is required to import the pool in read\-write mode. 76If this feature is not read-only compatible, support is also required to 77import the pool in read\-only mode (see "Read\-only compatibility"). 78.It Sy enabled 79An administrator has marked this feature as enabled on the pool, but the 80feature's on\-disk format changes have not been made yet. 81The pool can still be imported by software that does not support this feature, 82but changes may be made to the on\-disk format at any time which will move 83the feature to the 84.Sy active 85state. 86Some features may support returning to the 87.Sy enabled 88state after becoming 89.Sy active . 90See feature\-specific documentation for details. 91.It Sy disabled 92This feature's on\-disk format changes have not been made and will not be made 93unless an administrator moves the feature to the 94.Sy enabled 95state. 96Features cannot be disabled once they have been enabled. 97.El 98.Pp 99The state of supported features is exposed through pool properties of the form 100.Sy feature@short_name . 101.Ss Read\-only compatibility 102Some features may make on\-disk format changes that do not interfere with other 103software's ability to read from the pool. 104These features are referred to as "read\-only compatible". 105If all unsupported features on a pool are read\-only compatible, the pool can 106be imported in read\-only mode by setting the 107.Sy readonly 108property during import (see 109.Xr zpool 8 110for details on importing pools). 111.Ss Unsupported features 112For each unsupported feature enabled on an imported pool a pool property 113named 114.Sy unsupported@feature_guid 115will indicate why the import was allowed despite the unsupported feature. 116Possible values for this property are: 117.Bl -tag -width "XXXXXXXX" 118.It Sy inactive 119The feature is in the 120.Sy enabled 121state and therefore the pool's on\-disk format is still compatible with 122software that does not support this feature. 123.It Sy readonly 124The feature is read\-only compatible and the pool has been imported in 125read\-only mode. 126.El 127.Ss Feature dependencies 128Some features depend on other features being enabled in order to function 129properly. 130Enabling a feature will automatically enable any features it depends on. 131.Sh FEATURES 132The following features are supported on this system: 133.Bl -tag -width "XXXXXXXX" 134.It Sy async_destroy 135.Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:async_destroy" 136.It GUID Ta com.delphix:async_destroy 137.It READ\-ONLY COMPATIBLE Ta yes 138.It DEPENDENCIES Ta none 139.El 140.Pp 141Destroying a file system requires traversing all of its data in order to 142return its used space to the pool. 143Without 144.Sy async_destroy 145the file system is not fully removed until all space has been reclaimed. 146If the destroy operation is interrupted by a reboot or power outage the next 147attempt to open the pool will need to complete the destroy operation 148synchronously. 149.Pp 150When 151.Sy async_destroy 152is enabled the file system's data will be reclaimed by a background process, 153allowing the destroy operation to complete without traversing the entire file 154system. 155The background process is able to resume interrupted destroys after the pool 156has been opened, eliminating the need to finish interrupted destroys as part 157of the open operation. 158The amount of space remaining to be reclaimed by the background process is 159available through the 160.Sy freeing 161property. 162.Pp 163This feature is only 164.Sy active 165while 166.Sy freeing 167is non\-zero. 168.It Sy empty_bpobj 169.Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:empty_bpobj" 170.It GUID Ta com.delphix:empty_bpobj 171.It READ\-ONLY COMPATIBLE Ta yes 172.It DEPENDENCIES Ta none 173.El 174.Pp 175This feature increases the performance of creating and using a large number 176of snapshots of a single filesystem or volume, and also reduces the disk 177space required. 178.Pp 179When there are many snapshots, each snapshot uses many Block Pointer Objects 180.Pq bpobj's 181to track blocks associated with that snapshot. 182However, in common use cases, most of these bpobj's are empty. 183This feature allows us to create each bpobj on-demand, thus eliminating the 184empty bpobjs. 185.Pp 186This feature is 187.Sy active 188while there are any filesystems, volumes, or snapshots which were created 189after enabling this feature. 190.It Sy filesystem_limits 191.Bl -column "READ\-ONLY COMPATIBLE" "com.joyent:filesystem_limits" 192.It GUID Ta com.joyent:filesystem_limits 193.It READ\-ONLY COMPATIBLE Ta yes 194.It DEPENDENCIES Ta extensible_dataset 195.El 196.Pp 197This feature enables filesystem and snapshot limits. 198These limits can be used 199to control how many filesystems and/or snapshots can be created at the point in 200the tree on which the limits are set. 201.Pp 202This feature is 203.Sy active 204once either of the limit properties has been 205set on a dataset. 206Once activated the feature is never deactivated. 207.It Sy lz4_compress 208.Bl -column "READ\-ONLY COMPATIBLE" "org.illumos:lz4_compress" 209.It GUID Ta org.illumos:lz4_compress 210.It READ\-ONLY COMPATIBLE Ta no 211.It DEPENDENCIES Ta none 212.El 213.Pp 214.Sy lz4 215is a high-performance real-time compression algorithm that 216features significantly faster compression and decompression as well as a 217higher compression ratio than the older 218.Sy lzjb 219compression. 220Typically, 221.Sy lz4 222compression is approximately 50% faster on 223compressible data and 200% faster on incompressible data than 224.Sy lzjb . 225It is also approximately 80% faster on decompression, while 226giving approximately 10% better compression ratio. 227.Pp 228When the 229.Sy lz4_compress 230feature is set to 231.Sy enabled , 232the 233administrator can turn on 234.Sy lz4 235compression on any dataset on the 236pool using the 237.Xr zfs 8 238command. 239Also, all newly written metadata 240will be compressed with 241.Sy lz4 242algorithm. 243Since this feature is not read-only compatible, this 244operation will render the pool unimportable on systems without support 245for the 246.Sy lz4_compress 247feature. 248Booting off of 249.Sy lz4 250-compressed root pools is supported. 251.Pp 252This feature becomes 253.Sy active 254as soon as it is enabled and will 255never return to being 256.Sy enabled . 257.It Sy multi_vdev_crash_dump 258.Bl -column "READ\-ONLY COMPATIBLE" "com.joyent:multi_vdev_crash_dump" 259.It GUID Ta com.joyent:multi_vdev_crash_dump 260.It READ\-ONLY COMPATIBLE Ta no 261.It DEPENDENCIES Ta none 262.El 263.Pp 264This feature allows a dump device to be configured with a pool comprised 265of multiple vdevs. 266Those vdevs may be arranged in any mirrored or raidz 267configuration. 268.\" TODO: this is not yet supported on FreeBSD. 269.\" .Pp 270.\" When the 271.\" .Sy multi_vdev_crash_dump 272.\" feature is set to 273.\" .Sy enabled , 274.\" the administrator can use the 275.\" .Xr dumpon 8 276.\" command to configure a 277.\" dump device on a pool comprised of multiple vdevs. 278.It Sy spacemap_histogram 279.Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:spacemap_histogram" 280.It GUID Ta com.delphix:spacemap_histogram 281.It READ\-ONLY COMPATIBLE Ta yes 282.It DEPENDENCIES Ta none 283.El 284.Pp 285This features allows ZFS to maintain more information about how free space 286is organized within the pool. If this feature is 287.Sy enabled , 288ZFS will 289set this feature to 290.Sy active 291when a new space map object is created or 292an existing space map is upgraded to the new format. 293Once the feature is 294.Sy active , 295it will remain in that state until the pool is destroyed. 296.It Sy extensible_dataset 297.Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:extensible_dataset" 298.It GUID Ta com.delphix:extensible_dataset 299.It READ\-ONLY COMPATIBLE Ta no 300.It DEPENDENCIES Ta none 301.El 302.Pp 303This feature allows more flexible use of internal ZFS data structures, 304and exists for other features to depend on. 305.Pp 306This feature will be 307.Sy active 308when the first dependent feature uses it, 309and will be returned to the 310.Sy enabled 311state when all datasets that use 312this feature are destroyed. 313.It Sy bookmarks 314.Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:bookmarks" 315.It GUID Ta com.delphix:bookmarks 316.It READ\-ONLY COMPATIBLE Ta yes 317.It DEPENDENCIES Ta extensible_dataset 318.El 319.Pp 320This feature enables use of the 321.Nm zfs 322.Cm bookmark 323subcommand. 324.Pp 325This feature is 326.Sy active 327while any bookmarks exist in the pool. 328All bookmarks in the pool can be listed by running 329.Nm zfs 330.Cm list 331.Fl t No bookmark Fl r Ar poolname . 332.It Sy enabled_txg 333.Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:enabled_txg" 334.It GUID Ta com.delphix:enabled_txg 335.It READ\-ONLY COMPATIBLE Ta yes 336.It DEPENDENCIES Ta none 337.El 338.Pp 339Once this feature is enabled ZFS records the transaction group number 340in which new features are enabled. This has no user-visible impact, 341but other features may depend on this feature. 342.Pp 343This feature becomes 344.Sy active 345as soon as it is enabled and will 346never return to being 347.Sy enabled . 348.It Sy hole_birth 349.Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:hole_birth" 350.It GUID Ta com.delphix:hole_birth 351.It READ\-ONLY COMPATIBLE Ta no 352.It DEPENDENCIES Ta enabled_txg 353.El 354.Pp 355This feature improves performance of incremental sends 356.Pq Dq zfs send -i 357and receives for objects with many holes. 358The most common case of 359hole-filled objects is zvols. 360.Pp 361An incremental send stream from snapshot 362.Sy A 363to snapshot 364.Sy B 365contains information about every block that changed between 366.Sy A 367and 368.Sy B . 369Blocks which did not change between those snapshots can be 370identified and omitted from the stream using a piece of metadata called 371the 'block birth time', but birth times are not recorded for holes 372.Pq blocks filled only with zeroes . 373Since holes created after 374.Sy A 375cannot be 376distinguished from holes created before 377.Sy A , 378information about every 379hole in the entire filesystem or zvol is included in the send stream. 380.Pp 381For workloads where holes are rare this is not a problem. 382However, when 383incrementally replicating filesystems or zvols with many holes 384.Pq for example a zvol formatted with another filesystem 385a lot of time will 386be spent sending and receiving unnecessary information about holes that 387already exist on the receiving side. 388.Pp 389Once the 390.Sy hole_birth 391feature has been enabled the block birth times 392of all new holes will be recorded. 393Incremental sends between snapshots 394created after this feature is enabled will use this new metadata to avoid 395sending information about holes that already exist on the receiving side. 396.Pp 397This feature becomes 398.Sy active 399as soon as it is enabled and will 400never return to being 401.Sy enabled . 402.It Sy embedded_data 403.Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:embedded_data" 404.It GUID Ta com.delphix:embedded_data 405.It READ\-ONLY COMPATIBLE Ta no 406.It DEPENDENCIES Ta none 407.El 408.Pp 409This feature improves the performance and compression ratio of 410highly-compressible blocks. 411Blocks whose contents can compress to 112 bytes 412or smaller can take advantage of this feature. 413.Pp 414When this feature is enabled, the contents of highly-compressible blocks are 415stored in the block "pointer" itself 416.Po a misnomer in this case, as it contains 417the compressed data, rather than a pointer to its location on disk 418.Pc . 419Thus 420the space of the block 421.Pq one sector, typically 512 bytes or 4KB 422is saved, 423and no additional i/o is needed to read and write the data block. 424.Pp 425This feature becomes 426.Sy active 427as soon as it is enabled and will 428never return to being 429.Sy enabled . 430.It Sy large_blocks 431.Bl -column "READ\-ONLY COMPATIBLE" "org.open-zfs:large_block" 432.It GUID Ta org.open-zfs:large_block 433.It READ\-ONLY COMPATIBLE Ta no 434.It DEPENDENCIES Ta extensible_dataset 435.El 436.Pp 437The 438.Sy large_block 439feature allows the record size on a dataset to be 440set larger than 128KB. 441.Pp 442This feature becomes 443.Sy active 444once a 445.Sy recordsize 446property has been set larger than 128KB, and will return to being 447.Sy enabled 448once all filesystems that have ever had their recordsize larger than 128KB 449are destroyed. 450.Pp 451Please note that booting from datasets that have recordsize greater than 452128KB is 453.Em NOT 454supported by the 455.Fx 456boot loader. 457.It Sy sha512 458.Bl -column "READ\-ONLY COMPATIBLE" "org.illumos:sha512" 459.It GUID Ta org.illumos:sha512 460.It READ\-ONLY COMPATIBLE Ta no 461.It DEPENDENCIES Ta none 462.El 463.Pp 464The 465.Sy sha512 466feature enables the use of the SHA-512/256 truncated hash algorithm 467.Pq FIPS 180-4 468for checksum and dedup. 469The native 64-bit arithmetic of SHA-512 provides an approximate 50% 470performance boost over SHA-256 on 64-bit hardware and is thus a good 471minimum-change replacement candidate for systems where hash performance is 472important, but these systems cannot for whatever reason utilize the faster 473.Sy skein 474algorithms. 475.Pp 476When the 477.Sy sha512 478feature is set to 479.Sy enabled , 480the administrator can turn on the 481.Sy sha512 482checksum on any dataset using the 483.Dl # zfs set checksum=sha512 Ar dataset 484command. 485This feature becomes 486.Sy active 487once a 488.Sy checksum 489property has been set to 490.Sy sha512 , 491and will return to being 492.Sy enabled 493once all filesystems that have ever had their checksum set to 494.Sy sha512 495are destroyed. 496.Pp 497Booting off of a pools utilizing SHA-512/256 is 498.Em NOT 499yet supported. 500.It Sy skein 501.Bl -column "READ\-ONLY COMPATIBLE" "org.illumos:skein" 502.It GUID Ta org.illumos:skein 503.It READ\-ONLY COMPATIBLE Ta no 504.It DEPENDENCIES Ta none 505.El 506.Pp 507The 508.Sy skein 509feature enables the use of the Skein hash algorithm for checksum and dedup. 510Skein is a high-performance secure hash algorithm that was a finalist in the 511NIST SHA-3 competition. 512It provides a very high security margin and high performance on 64-bit hardware 513.Pq 80% faster than SHA-256 . 514This implementation also utilizes the new salted checksumming functionality in 515ZFS, which means that the checksum is pre-seeded with a secret 256-bit random 516key 517.Pq stored on the pool 518before being fed the data block to be checksummed. 519Thus the produced checksums are unique to a given pool, preventing hash 520collision attacks on systems with dedup. 521.Pp 522When the 523.Sy skein 524feature is set to 525.Sy enabled , 526the administrator can turn on the 527.Sy skein 528checksum on any dataset using the 529.Dl # zfs set checksum=skein Ar dataset 530command. 531This feature becomes 532.Sy active 533once a 534.Sy checksum 535property has been set to 536.Sy skein , 537and will return to being 538.Sy enabled 539once all filesystems that have ever had their checksum set to 540.Sy skein 541are destroyed. 542.Pp 543Booting off of pools using 544.Sy skein 545is 546.Em NOT 547supported. 548.El 549.Sh SEE ALSO 550.Xr zpool 8 551.Sh AUTHORS 552This manual page is a 553.Xr mdoc 7 554reimplementation of the 555.Tn illumos 556manual page 557.Em zpool-features(5) , 558modified and customized for 559.Fx 560and licensed under the Common Development and Distribution License 561.Pq Tn CDDL . 562.Pp 563The 564.Xr mdoc 7 565implementation of this manual page was initially written by 566.An Martin Matuska Aq mm@FreeBSD.org . 567