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NEX-6088 ZFS scrub/resilver take excessively long due to issuing lots of random IO (reverting a mismerge in zpool-features.5)
NEX-6088 ZFS scrub/resilver take excessively long due to issuing lots of random IO
Reviewed by: Roman Strashkin <roman.strashkin@nexenta.com>
Reviewed by: Sanjay Nadkarni <sanjay.nadkarni@nexenta.com>
NEX-6197 Description of feature@wbc is incorrect
Reviewed by: Alex Aizman <alex.aizman@nexenta.com>
Reviewed by: Saso Kiselkov <saso.kiselkov@nexenta.com>
NEX-4584 System panic when adding special vdev to a pool that does not support feature flags
Reviewed by: Alex Aizman <alex.aizman@nexenta.com>
Reviewed by: Josef 'Jeff' Sipek <josef.sipek@nexenta.com>
Reviewed by: Saso Kiselkov <saso.kiselkov@nexenta.com>
Reviewed by: Steve Peng <steve.peng@nexenta.com>
NEX-5795 Rename 'wrc' as 'wbc' in the source and in the tech docs
Reviewed by: Alex Aizman <alex.aizman@nexenta.com>
Reviewed by: Sanjay Nadkarni <sanjay.nadkarni@nexenta.com>
Reviewed by: Alek Pinchuk <alek.pinchuk@nexenta.com>
4185 add new cryptographic checksums to ZFS: SHA-512, Skein, Edon-R (fix studio build)
4185 add new cryptographic checksums to ZFS: SHA-512, Skein, Edon-R
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Saso Kiselkov <saso.kiselkov@nexenta.com>
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Approved by: Garrett D'Amore <garrett@damore.org>
NEX-4476 WRC: Allow to use write back cache per tree of datasets
Reviewed by: Alek Pinchuk <alek.pinchuk@nexenta.com>
Reviewed by: Alex Aizman <alex.aizman@nexenta.com>
Revert "NEX-4476 WRC: Allow to use write back cache per tree of datasets"
This reverts commit fe97b74444278a6f36fec93179133641296312da.
NEX-4476 WRC: Allow to use write back cache per tree of datasets
Reviewed by: Alek Pinchuk <alek.pinchuk@nexenta.com>
Reviewed by: Alex Aizman <alex.aizman@nexenta.com>
SUP-817 Removed references to special device from man and help
Revert "SUP-817 Removed references to special device"
This reverts commit f8970e28f0d8bd6b69711722f341e3e1d0e1babf.
SUP-817 Removed references to special device
4370 avoid transmitting holes during zfs send
4371 DMU code clean up
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
Approved by: Garrett D'Amore <garrett@damore.org>
OS-102 add man page info and tests for vdev/CoS properties and ZFS meta features
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--- old/usr/src/man/man5/zpool-features.5
+++ new/usr/src/man/man5/zpool-features.5
1 1 '\" te
2 2 .\" Copyright (c) 2013, 2016 by Delphix. All rights reserved.
3 3 .\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
4 4 .\" Copyright (c) 2014, Joyent, Inc. All rights reserved.
5 5 .\" Copyright (c) 2014 Integros [integros.com]
6 +.\" Copyright (c) 2016, Nexenta Systems, Inc. All rights reserved.
6 7 .\" The contents of this file are subject to the terms of the Common Development
7 8 .\" and Distribution License (the "License"). You may not use this file except
8 9 .\" in compliance with the License. You can obtain a copy of the license at
9 10 .\" usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.
10 11 .\"
11 12 .\" See the License for the specific language governing permissions and
12 13 .\" limitations under the License. When distributing Covered Code, include this
13 14 .\" CDDL HEADER in each file and include the License file at
14 15 .\" usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this
15 16 .\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your
16 17 .\" own identifying information:
17 18 .\" Portions Copyright [yyyy] [name of copyright owner]
18 -.TH ZPOOL-FEATURES 5 "Aug 27, 2013"
19 +.TH ZPOOL-FEATURES 5 "Mar 25, 2016"
19 20 .SH NAME
20 21 zpool\-features \- ZFS pool feature descriptions
21 22 .SH DESCRIPTION
22 23 .LP
23 24 ZFS pool on\-disk format versions are specified via "features" which replace
24 25 the old on\-disk format numbers (the last supported on\-disk format number is
25 26 28). To enable a feature on a pool use the \fBupgrade\fR subcommand of the
26 27 \fBzpool\fR(1M) command, or set the \fBfeature@\fR\fIfeature_name\fR property
27 28 to \fBenabled\fR.
28 29 .sp
29 30 .LP
30 31 The pool format does not affect file system version compatibility or the ability
31 32 to send file systems between pools.
32 33 .sp
33 34 .LP
34 35 Since most features can be enabled independently of each other the on\-disk
35 36 format of the pool is specified by the set of all features marked as
36 37 \fBactive\fR on the pool. If the pool was created by another software version
37 38 this set may include unsupported features.
38 39 .SS "Identifying features"
39 40 .LP
40 41 Every feature has a guid of the form \fIcom.example:feature_name\fR. The reverse
41 42 DNS name ensures that the feature's guid is unique across all ZFS
42 43 implementations. When unsupported features are encountered on a pool they will
43 44 be identified by their guids. Refer to the documentation for the ZFS
44 45 implementation that created the pool for information about those features.
45 46 .sp
46 47 .LP
47 48 Each supported feature also has a short name. By convention a feature's short
48 49 name is the portion of its guid which follows the ':' (e.g.
49 50 \fIcom.example:feature_name\fR would have the short name \fIfeature_name\fR),
50 51 however a feature's short name may differ across ZFS implementations if
51 52 following the convention would result in name conflicts.
52 53 .SS "Feature states"
53 54 .LP
54 55 Features can be in one of three states:
55 56 .sp
56 57 .ne 2
57 58 .na
58 59 \fB\fBactive\fR\fR
59 60 .ad
60 61 .RS 12n
61 62 This feature's on\-disk format changes are in effect on the pool. Support for
62 63 this feature is required to import the pool in read\-write mode. If this
63 64 feature is not read-only compatible, support is also required to import the pool
64 65 in read\-only mode (see "Read\-only compatibility").
65 66 .RE
66 67
67 68 .sp
68 69 .ne 2
69 70 .na
70 71 \fB\fBenabled\fR\fR
71 72 .ad
72 73 .RS 12n
73 74 An administrator has marked this feature as enabled on the pool, but the
74 75 feature's on\-disk format changes have not been made yet. The pool can still be
75 76 imported by software that does not support this feature, but changes may be made
76 77 to the on\-disk format at any time which will move the feature to the
77 78 \fBactive\fR state. Some features may support returning to the \fBenabled\fR
78 79 state after becoming \fBactive\fR. See feature\-specific documentation for
79 80 details.
80 81 .RE
81 82
82 83 .sp
83 84 .ne 2
84 85 .na
85 86 \fBdisabled\fR
86 87 .ad
87 88 .RS 12n
88 89 This feature's on\-disk format changes have not been made and will not be made
89 90 unless an administrator moves the feature to the \fBenabled\fR state. Features
90 91 cannot be disabled once they have been enabled.
91 92 .RE
92 93
93 94 .sp
94 95 .LP
95 96 The state of supported features is exposed through pool properties of the form
96 97 \fIfeature@short_name\fR.
97 98 .SS "Read\-only compatibility"
98 99 .LP
99 100 Some features may make on\-disk format changes that do not interfere with other
100 101 software's ability to read from the pool. These features are referred to as
101 102 "read\-only compatible". If all unsupported features on a pool are read\-only
102 103 compatible, the pool can be imported in read\-only mode by setting the
103 104 \fBreadonly\fR property during import (see \fBzpool\fR(1M) for details on
104 105 importing pools).
105 106 .SS "Unsupported features"
106 107 .LP
107 108 For each unsupported feature enabled on an imported pool a pool property
108 109 named \fIunsupported@feature_guid\fR will indicate why the import was allowed
109 110 despite the unsupported feature. Possible values for this property are:
110 111
111 112 .sp
112 113 .ne 2
113 114 .na
114 115 \fB\fBinactive\fR\fR
115 116 .ad
116 117 .RS 12n
117 118 The feature is in the \fBenabled\fR state and therefore the pool's on\-disk
118 119 format is still compatible with software that does not support this feature.
119 120 .RE
120 121
121 122 .sp
122 123 .ne 2
123 124 .na
124 125 \fB\fBreadonly\fR\fR
125 126 .ad
126 127 .RS 12n
127 128 The feature is read\-only compatible and the pool has been imported in
128 129 read\-only mode.
129 130 .RE
130 131
131 132 .SS "Feature dependencies"
132 133 .LP
133 134 Some features depend on other features being enabled in order to function
134 135 properly. Enabling a feature will automatically enable any features it
135 136 depends on.
136 137 .SH FEATURES
137 138 .LP
138 139 The following features are supported on this system:
139 140 .sp
140 141 .ne 2
141 142 .na
142 143 \fB\fBasync_destroy\fR\fR
143 144 .ad
144 145 .RS 4n
145 146 .TS
146 147 l l .
147 148 GUID com.delphix:async_destroy
148 149 READ\-ONLY COMPATIBLE yes
149 150 DEPENDENCIES none
150 151 .TE
151 152
152 153 Destroying a file system requires traversing all of its data in order to
153 154 return its used space to the pool. Without \fBasync_destroy\fR the file system
154 155 is not fully removed until all space has been reclaimed. If the destroy
155 156 operation is interrupted by a reboot or power outage the next attempt to open
156 157 the pool will need to complete the destroy operation synchronously.
157 158
158 159 When \fBasync_destroy\fR is enabled the file system's data will be reclaimed
159 160 by a background process, allowing the destroy operation to complete without
160 161 traversing the entire file system. The background process is able to resume
161 162 interrupted destroys after the pool has been opened, eliminating the need
162 163 to finish interrupted destroys as part of the open operation. The amount
163 164 of space remaining to be reclaimed by the background process is available
164 165 through the \fBfreeing\fR property.
165 166
166 167 This feature is only \fBactive\fR while \fBfreeing\fR is non\-zero.
167 168 .RE
168 169
169 170 .sp
170 171 .ne 2
171 172 .na
172 173 \fB\fBempty_bpobj\fR\fR
173 174 .ad
174 175 .RS 4n
175 176 .TS
176 177 l l .
177 178 GUID com.delphix:empty_bpobj
178 179 READ\-ONLY COMPATIBLE yes
179 180 DEPENDENCIES none
180 181 .TE
181 182
182 183 This feature increases the performance of creating and using a large
183 184 number of snapshots of a single filesystem or volume, and also reduces
184 185 the disk space required.
185 186
186 187 When there are many snapshots, each snapshot uses many Block Pointer
187 188 Objects (bpobj's) to track blocks associated with that snapshot.
188 189 However, in common use cases, most of these bpobj's are empty. This
189 190 feature allows us to create each bpobj on-demand, thus eliminating the
190 191 empty bpobjs.
191 192
192 193 This feature is \fBactive\fR while there are any filesystems, volumes,
193 194 or snapshots which were created after enabling this feature.
194 195 .RE
195 196
196 197 .sp
197 198 .ne 2
198 199 .na
199 200 \fB\fBfilesystem_limits\fR\fR
200 201 .ad
201 202 .RS 4n
202 203 .TS
203 204 l l .
204 205 GUID com.joyent:filesystem_limits
205 206 READ\-ONLY COMPATIBLE yes
206 207 DEPENDENCIES extensible_dataset
207 208 .TE
208 209
209 210 This feature enables filesystem and snapshot limits. These limits can be used
210 211 to control how many filesystems and/or snapshots can be created at the point in
211 212 the tree on which the limits are set.
212 213
213 214 This feature is \fBactive\fR once either of the limit properties has been
214 215 set on a dataset. Once activated the feature is never deactivated.
215 216 .RE
216 217
217 218 .sp
218 219 .ne 2
219 220 .na
220 221 \fB\fBlz4_compress\fR\fR
221 222 .ad
222 223 .RS 4n
223 224 .TS
224 225 l l .
225 226 GUID org.illumos:lz4_compress
226 227 READ\-ONLY COMPATIBLE no
227 228 DEPENDENCIES none
228 229 .TE
229 230
230 231 \fBlz4\fR is a high-performance real-time compression algorithm that
231 232 features significantly faster compression and decompression as well as a
232 233 higher compression ratio than the older \fBlzjb\fR compression.
233 234 Typically, \fBlz4\fR compression is approximately 50% faster on
234 235 compressible data and 200% faster on incompressible data than
235 236 \fBlzjb\fR. It is also approximately 80% faster on decompression, while
236 237 giving approximately 10% better compression ratio.
237 238
238 239 When the \fBlz4_compress\fR feature is set to \fBenabled\fR, the
239 240 administrator can turn on \fBlz4\fR compression on any dataset on the
240 241 pool using the \fBzfs\fR(1M) command. Also, all newly written metadata
241 242 will be compressed with \fBlz4\fR algorithm. Since this feature is not
242 243 read-only compatible, this operation will render the pool unimportable
243 244 on systems without support for the \fBlz4_compress\fR feature. Booting
244 245 off of \fBlz4\fR-compressed root pools is supported.
245 246
246 247 This feature becomes \fBactive\fR as soon as it is enabled and will
247 248 never return to being \fBenabled\fR.
248 249 .RE
249 250
250 251 .sp
251 252 .ne 2
252 253 .na
253 254 \fB\fBspacemap_histogram\fR\fR
254 255 .ad
255 256 .RS 4n
256 257 .TS
257 258 l l .
258 259 GUID com.delphix:spacemap_histogram
259 260 READ\-ONLY COMPATIBLE yes
260 261 DEPENDENCIES none
261 262 .TE
262 263
263 264 This features allows ZFS to maintain more information about how free space
264 265 is organized within the pool. If this feature is \fBenabled\fR, ZFS will
265 266 set this feature to \fBactive\fR when a new space map object is created or
266 267 an existing space map is upgraded to the new format. Once the feature is
267 268 \fBactive\fR, it will remain in that state until the pool is destroyed.
268 269 .RE
269 270
270 271 .sp
271 272 .ne 2
272 273 .na
273 274 \fB\fBmulti_vdev_crash_dump\fR\fR
274 275 .ad
275 276 .RS 4n
276 277 .TS
277 278 l l .
278 279 GUID com.joyent:multi_vdev_crash_dump
279 280 READ\-ONLY COMPATIBLE no
280 281 DEPENDENCIES none
281 282 .TE
282 283
283 284 This feature allows a dump device to be configured with a pool comprised
284 285 of multiple vdevs. Those vdevs may be arranged in any mirrored or raidz
285 286 configuration.
286 287
287 288 When the \fBmulti_vdev_crash_dump\fR feature is set to \fBenabled\fR,
288 289 the administrator can use the \fBdumpadm\fR(1M) command to configure a
289 290 dump device on a pool comprised of multiple vdevs.
290 291 .RE
291 292
292 293 .sp
293 294 .ne 2
294 295 .na
295 296 \fB\fBextensible_dataset\fR\fR
296 297 .ad
297 298 .RS 4n
298 299 .TS
299 300 l l .
300 301 GUID com.delphix:extensible_dataset
301 302 READ\-ONLY COMPATIBLE no
302 303 DEPENDENCIES none
303 304 .TE
304 305
305 306 This feature allows more flexible use of internal ZFS data structures,
306 307 and exists for other features to depend on.
307 308
308 309 This feature will be \fBactive\fR when the first dependent feature uses it,
309 310 and will be returned to the \fBenabled\fR state when all datasets that use
310 311 this feature are destroyed.
311 312
312 313 .RE
313 314
314 315 .sp
315 316 .ne 2
316 317 .na
317 318 \fB\fBbookmarks\fR\fR
318 319 .ad
319 320 .RS 4n
320 321 .TS
321 322 l l .
322 323 GUID com.delphix:bookmarks
323 324 READ\-ONLY COMPATIBLE yes
324 325 DEPENDENCIES extensible_dataset
325 326 .TE
326 327
327 328 This feature enables use of the \fBzfs bookmark\fR subcommand.
328 329
329 330 This feature is \fBactive\fR while any bookmarks exist in the pool.
330 331 All bookmarks in the pool can be listed by running
331 332 \fBzfs list -t bookmark -r \fIpoolname\fR\fR.
332 333
333 334 .RE
334 335
335 336 .sp
336 337 .ne 2
337 338 .na
338 339 \fB\fBenabled_txg\fR\fR
339 340 .ad
340 341 .RS 4n
341 342 .TS
342 343 l l .
343 344 GUID com.delphix:enabled_txg
344 345 READ\-ONLY COMPATIBLE yes
345 346 DEPENDENCIES none
346 347 .TE
347 348
348 349 Once this feature is enabled ZFS records the transaction group number
349 350 in which new features are enabled. This has no user-visible impact,
350 351 but other features may depend on this feature.
351 352
352 353 This feature becomes \fBactive\fR as soon as it is enabled and will
353 354 never return to being \fBenabled\fR.
354 355
355 356 .RE
356 357
357 358 .sp
358 359 .ne 2
359 360 .na
360 361 \fB\fBhole_birth\fR\fR
361 362 .ad
362 363 .RS 4n
363 364 .TS
364 365 l l .
365 366 GUID com.delphix:hole_birth
366 367 READ\-ONLY COMPATIBLE no
367 368 DEPENDENCIES enabled_txg
368 369 .TE
369 370
370 371 This feature improves performance of incremental sends ("zfs send -i")
371 372 and receives for objects with many holes. The most common case of
372 373 hole-filled objects is zvols.
373 374
374 375 An incremental send stream from snapshot \fBA\fR to snapshot \fBB\fR
375 376 contains information about every block that changed between \fBA\fR and
376 377 \fBB\fR. Blocks which did not change between those snapshots can be
377 378 identified and omitted from the stream using a piece of metadata called
378 379 the 'block birth time', but birth times are not recorded for holes (blocks
379 380 filled only with zeroes). Since holes created after \fBA\fR cannot be
380 381 distinguished from holes created before \fBA\fR, information about every
381 382 hole in the entire filesystem or zvol is included in the send stream.
382 383
383 384 For workloads where holes are rare this is not a problem. However, when
384 385 incrementally replicating filesystems or zvols with many holes (for
385 386 example a zvol formatted with another filesystem) a lot of time will
386 387 be spent sending and receiving unnecessary information about holes that
387 388 already exist on the receiving side.
388 389
389 390 Once the \fBhole_birth\fR feature has been enabled the block birth times
390 391 of all new holes will be recorded. Incremental sends between snapshots
391 392 created after this feature is enabled will use this new metadata to avoid
392 393 sending information about holes that already exist on the receiving side.
393 394
394 395 This feature becomes \fBactive\fR as soon as it is enabled and will
395 396 never return to being \fBenabled\fR.
396 397
397 398 .RE
398 399
399 400 .sp
400 401 .ne 2
401 402 .na
402 403 \fB\fBembedded_data\fR\fR
403 404 .ad
404 405 .RS 4n
405 406 .TS
406 407 l l .
407 408 GUID com.delphix:embedded_data
408 409 READ\-ONLY COMPATIBLE no
409 410 DEPENDENCIES none
410 411 .TE
411 412
412 413 This feature improves the performance and compression ratio of
413 414 highly-compressible blocks. Blocks whose contents can compress to 112 bytes
414 415 or smaller can take advantage of this feature.
415 416
416 417 When this feature is enabled, the contents of highly-compressible blocks are
417 418 stored in the block "pointer" itself (a misnomer in this case, as it contains
418 419 the compresseed data, rather than a pointer to its location on disk). Thus
419 420 the space of the block (one sector, typically 512 bytes or 4KB) is saved,
420 421 and no additional i/o is needed to read and write the data block.
421 422
422 423 This feature becomes \fBactive\fR as soon as it is enabled and will
423 424 never return to being \fBenabled\fR.
424 425
425 426 .RE
426 427
427 428 .sp
428 429 .ne 2
429 430 .na
430 431 \fB\fBdevice_removal\fR\fR
431 432 .ad
432 433 .RS 4n
433 434 .TS
434 435 l l .
435 436 GUID com.delphix:device_removal
436 437 READ\-ONLY COMPATIBLE no
437 438 DEPENDENCIES none
438 439 .TE
439 440
440 441 This feature enables the "zpool remove" subcommand to remove top-level
441 442 vdevs, evacuating them to reduce the total size of the pool.
442 443
443 444 This feature becomes \fBactive\fR when the "zpool remove" command is used
444 445 on a top-level vdev, and will never return to being \fBenabled\fR.
445 446
446 447 .RE
447 448 .sp
448 449 .ne 2
449 450 .na
450 451 \fB\fBobsolete_counts\fR\fR
451 452 .ad
452 453 .RS 4n
453 454 .TS
454 455 l l .
455 456 GUID com.delphix:obsolete_counts
456 457 READ\-ONLY COMPATIBLE yes
457 458 DEPENDENCIES device_removal
458 459 .TE
459 460
460 461 This feature is an enhancement of device_removal, which will over time
461 462 reduce the memory used to track removed devices. When indirect blocks
462 463 are freed or remapped, we note that their part of the indirect mapping
463 464 is "obsolete", i.e. no longer needed. See also the \fBzfs remap\fR
464 465 subcommand in \fBzfs\fR(1M).
465 466
466 467 This feature becomes \fBactive\fR when the "zpool remove" command is
467 468 used on a top-level vdev, and will never return to being \fBenabled\fR.
468 469
469 470 .RE
470 471 .sp
471 472 .ne 2
472 473 .na
473 474 \fB\fBlarge_blocks\fR\fR
474 475 .ad
475 476 .RS 4n
476 477 .TS
477 478 l l .
478 479 GUID org.open-zfs:large_block
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479 480 READ\-ONLY COMPATIBLE no
480 481 DEPENDENCIES extensible_dataset
481 482 .TE
482 483
483 484 The \fBlarge_block\fR feature allows the record size on a dataset to be
484 485 set larger than 128KB.
485 486
486 487 This feature becomes \fBactive\fR once a \fBrecordsize\fR property has been
487 488 set larger than 128KB, and will return to being \fBenabled\fR once all
488 489 filesystems that have ever had their recordsize larger than 128KB are destroyed.
490 +
489 491 .RE
490 492
493 +.sp
494 +.ne 2
495 +.na
496 +\fB\fBvdev_properties\fR\fR
497 +.ad
498 +.RS 4n
499 +.TS
500 +l l .
501 +GUID com.nexenta:vdev_properties
502 +READ\-ONLY COMPATIBLE yes
503 +DEPENDENCIES none
504 +.TE
505 +
506 +This feature indicates that the pool includes on-disk format changes that
507 +support persistent vdev-specific properties. This feature will be
508 +\fBactive\fR when the first vdev-specific property is set.
509 +
510 +.RE
511 +
512 +.sp
513 +.ne 2
514 +.na
515 +\fB\fBcos_properties\fR\fR
516 +.ad
517 +.RS 4n
518 +.TS
519 +l l .
520 +GUID com.nexenta:cos_properties
521 +READ\-ONLY COMPATIBLE yes
522 +DEPENDENCIES com.nexenta:vdev_properties
523 +.TE
524 +
525 +This feature indicates that the pool includes on-disk format changes that
526 +support persistent Class of Storage (CoS) properties. Such properties can
527 +be associated with a collection of device that belong to a common class
528 +from storage management standpoint. This feature will be
529 +\fBactive\fR when the first CoS property is set.
530 +
531 +.RE
532 +
533 +.sp
534 +.ne 2
535 +.na
536 +\fB\fBmeta_devices\fR\fR
537 +.ad
538 +.RS 4n
539 +.TS
540 +l l .
541 +GUID com.nexenta:meta_devices
542 +READ\-ONLY COMPATIBLE yes
543 +DEPENDENCIES none
544 +.TE
545 +
546 +This feature flag indicates presence of special-vdev in the pool. Special
547 +vdev is used to speed-up read and write operations and can be used to store
548 +ZFS metadata and/or write log (ZIL). In addition, special vdev can function
549 +as a writeback cache (WBC) within the pool, accelerating ZFS writes via
550 +underlying fast media (typically, write-optimized SSD).
551 +
552 +Note that unlike the first two functions the WBC function is configurable
553 +on a per-dataset tree basis.
554 +
555 +.RE
556 +
557 +.sp
558 +.ne 2
559 +.na
560 +\fB\fBwbc\fR\fR
561 +.ad
562 +.RS 4n
563 +.TS
564 +l l .
565 +GUID com.nexenta:wbc
566 +READ\-ONLY COMPATIBLE no
567 +DEPENDENCIES com.nexenta:meta_devices
568 +.TE
569 +
570 +When enabled, this feature indicates that the pool supports writeback caching.
571 +The latter can be activated on a specific filesystem (and all its children) or
572 +a volume (zvol) within the pool by setting the corresponding \fBwbc_mode\fR
573 +property to 'on'. This feature will show up as \fBdisabled\fR if the pool does
574 +not contain special-vdev.
575 +
576 +.RE
577 +
491 578 .sp
492 579 .ne 2
493 580 .na
494 581 \fB\fBsha512\fR\fR
495 582 .ad
496 583 .RS 4n
497 584 .TS
498 585 l l .
499 586 GUID org.illumos:sha512
500 587 READ\-ONLY COMPATIBLE no
501 588 DEPENDENCIES extensible_dataset
502 589 .TE
503 590
504 591 This feature enables the use of the SHA-512/256 truncated hash algorithm
505 592 (FIPS 180-4) for checksum and dedup. The native 64-bit arithmetic of
506 593 SHA-512 provides an approximate 50% performance boost over SHA-256 on
507 594 64-bit hardware and is thus a good minimum-change replacement candidate
508 595 for systems where hash performance is important, but these systems
509 596 cannot for whatever reason utilize the faster \fBskein\fR and
510 597 \fBedonr\fR algorithms.
511 598
512 599 When the \fBsha512\fR feature is set to \fBenabled\fR, the administrator
513 600 can turn on the \fBsha512\fR checksum on any dataset using the
514 601 \fBzfs set checksum=sha512\fR command. This feature becomes
515 602 \fBactive\fR once a \fBchecksum\fR property has been set to \fBsha512\fR,
516 603 and will return to being \fBenabled\fR once all filesystems that have
517 604 ever had their checksum set to \fBsha512\fR are destroyed.
518 605
519 606 Booting off of pools utilizing SHA-512/256 is supported (provided that
520 607 the updated GRUB stage2 module is installed).
521 608
522 609 .RE
523 610
524 611 .sp
525 612 .ne 2
526 613 .na
527 614 \fB\fBskein\fR\fR
528 615 .ad
529 616 .RS 4n
530 617 .TS
531 618 l l .
532 619 GUID org.illumos:skein
533 620 READ\-ONLY COMPATIBLE no
534 621 DEPENDENCIES extensible_dataset
535 622 .TE
536 623
537 624 This feature enables the use of the Skein hash algorithm for checksum
538 625 and dedup. Skein is a high-performance secure hash algorithm that was a
539 626 finalist in the NIST SHA-3 competition. It provides a very high security
540 627 margin and high performance on 64-bit hardware (80% faster than
541 628 SHA-256). This implementation also utilizes the new salted checksumming
542 629 functionality in ZFS, which means that the checksum is pre-seeded with a
543 630 secret 256-bit random key (stored on the pool) before being fed the data
544 631 block to be checksummed. Thus the produced checksums are unique to a
545 632 given pool, preventing hash collision attacks on systems with dedup.
546 633
547 634 When the \fBskein\fR feature is set to \fBenabled\fR, the administrator
548 635 can turn on the \fBskein\fR checksum on any dataset using the
549 636 \fBzfs set checksum=skein\fR command. This feature becomes
550 637 \fBactive\fR once a \fBchecksum\fR property has been set to \fBskein\fR,
551 638 and will return to being \fBenabled\fR once all filesystems that have
552 639 ever had their checksum set to \fBskein\fR are destroyed.
553 640
554 641 Booting off of pools using \fBskein\fR is \fBNOT\fR supported
555 642 -- any attempt to enable \fBskein\fR on a root pool will fail with an
556 643 error.
557 644
558 645 .RE
559 646
560 647 .sp
561 648 .ne 2
562 649 .na
563 650 \fB\fBedonr\fR\fR
564 651 .ad
565 652 .RS 4n
566 653 .TS
567 654 l l .
568 655 GUID org.illumos:edonr
569 656 READ\-ONLY COMPATIBLE no
570 657 DEPENDENCIES extensible_dataset
571 658 .TE
572 659
573 660 This feature enables the use of the Edon-R hash algorithm for checksum,
574 661 including for nopwrite (if compression is also enabled, an overwrite of
575 662 a block whose checksum matches the data being written will be ignored).
576 663 In an abundance of caution, Edon-R can not be used with dedup
577 664 (without verification).
578 665
579 666 Edon-R is a very high-performance hash algorithm that was part
580 667 of the NIST SHA-3 competition. It provides extremely high hash
581 668 performance (over 350% faster than SHA-256), but was not selected
582 669 because of its unsuitability as a general purpose secure hash algorithm.
583 670 This implementation utilizes the new salted checksumming functionality
584 671 in ZFS, which means that the checksum is pre-seeded with a secret
585 672 256-bit random key (stored on the pool) before being fed the data block
586 673 to be checksummed. Thus the produced checksums are unique to a given
587 674 pool.
588 675
589 676 When the \fBedonr\fR feature is set to \fBenabled\fR, the administrator
590 677 can turn on the \fBedonr\fR checksum on any dataset using the
591 678 \fBzfs set checksum=edonr\fR command. This feature becomes
592 679 \fBactive\fR once a \fBchecksum\fR property has been set to \fBedonr\fR,
593 680 and will return to being \fBenabled\fR once all filesystems that have
594 681 ever had their checksum set to \fBedonr\fR are destroyed.
595 682
596 683 Booting off of pools using \fBedonr\fR is \fBNOT\fR supported
597 684 -- any attempt to enable \fBedonr\fR on a root pool will fail with an
598 685 error.
599 686
600 687 .SH "SEE ALSO"
601 688 \fBzfs\fR(1M), \fBzpool\fR(1M)
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