1 '\" te 2 .\" Copyright (c) 2013 by Delphix. All rights reserved. 3 .\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved. 4 .\" Copyright (c) 2013, 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. 9 .\" 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" 18 .SH NAME 19 zpool\-features \- ZFS pool feature descriptions 20 .SH DESCRIPTION 21 .sp 22 .LP 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(1M) command, or set the \fBfeature@\fR\fIfeature_name\fR property 27 to \fBenabled\fR. 28 .sp 29 .LP 30 The pool format does not affect file system version compatibility or the ability 31 to send file systems between pools. 32 .sp 33 .LP 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" 39 .sp 40 .LP 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. 46 .sp 47 .LP 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. 53 .SS "Feature states" 54 .sp 55 .LP 56 Features can be in one of three states: 57 .sp 58 .ne 2 59 .na 60 \fB\fBactive\fR\fR 61 .ad 62 .RS 12n 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"). 67 .RE 68 69 .sp 70 .ne 2 71 .na 72 \fB\fBenabled\fR\fR 73 .ad 74 .RS 12n 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 81 details. 82 .RE 83 84 .sp 85 .ne 2 86 .na 87 \fBdisabled\fR 88 .ad 89 .RS 12n 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. 93 .RE 94 95 .sp 96 .LP 97 The state of supported features is exposed through pool properties of the form 98 \fIfeature@short_name\fR. 99 .SS "Read\-only compatibility" 100 .sp 101 .LP 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(1M) for details on 107 importing pools). 108 .SS "Unsupported features" 109 .sp 110 .LP 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: 114 115 .sp 116 .ne 2 117 .na 118 \fB\fBinactive\fR\fR 119 .ad 120 .RS 12n 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. 123 .RE 124 125 .sp 126 .ne 2 127 .na 128 \fB\fBreadonly\fR\fR 129 .ad 130 .RS 12n 131 The feature is read\-only compatible and the pool has been imported in 132 read\-only mode. 133 .RE 134 135 .SS "Feature dependencies" 136 .sp 137 .LP 138 Some features depend on other features being enabled in order to function 139 properly. Enabling a feature will automatically enable any features it 140 depends on. 141 .SH FEATURES 142 .sp 143 .LP 144 The following features are supported on this system: 145 .sp 146 .ne 2 147 .na 148 \fB\fBasync_destroy\fR\fR 149 .ad 150 .RS 4n 151 .TS 152 l l . 153 GUID com.delphix:async_destroy 154 READ\-ONLY COMPATIBLE yes 155 DEPENDENCIES none 156 .TE 157 158 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. 163 164 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. 171 172 This feature is only \fBactive\fR while \fBfreeing\fR is non\-zero. 173 .RE 174 175 .sp 176 .ne 2 177 .na 178 \fB\fBempty_bpobj\fR\fR 179 .ad 180 .RS 4n 181 .TS 182 l l . 183 GUID com.delphix:empty_bpobj 184 READ\-ONLY COMPATIBLE yes 185 DEPENDENCIES none 186 .TE 187 188 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. 191 192 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 196 empty bpobjs. 197 198 This feature is \fBactive\fR while there are any filesystems, volumes, 199 or snapshots which were created after enabling this feature. 200 .RE 201 202 .sp 203 .ne 2 204 .na 205 \fB\fBlz4_compress\fR\fR 206 .ad 207 .RS 4n 208 .TS 209 l l . 210 GUID org.illumos:lz4_compress 211 READ\-ONLY COMPATIBLE no 212 DEPENDENCIES none 213 .TE 214 215 \fBlz4\fR is a high-performance real-time compression algorithm that 216 features significantly faster compression and decompression as well as a 217 higher compression ratio than the older \fBlzjb\fR compression. 218 Typically, \fBlz4\fR compression is approximately 50% faster on 219 compressible data and 200% faster on incompressible data than 220 \fBlzjb\fR. It is also approximately 80% faster on decompression, while 221 giving approximately 10% better compression ratio. 222 223 When the \fBlz4_compress\fR feature is set to \fBenabled\fR, the 224 administrator can turn on \fBlz4\fR compression on any dataset on the 225 pool using the \fBzfs\fR(1M) command. Please note that doing so will 226 immediately activate the \fBlz4_compress\fR feature on the underlying 227 pool (even before any data is written). Since this feature is not 228 read-only compatible, this operation will render the pool unimportable 229 on systems without support for the \fBlz4_compress\fR feature. At the 230 moment, this operation cannot be reversed. Booting off of 231 \fBlz4\fR-compressed root pools is supported. 232 .RE 233 234 .sp 235 .ne 2 236 .na 237 \fB\fBspacemap_histogram\fR\fR 238 .ad 239 .RS 4n 240 .TS 241 l l . 242 GUID com.delphix:spacemap_histogram 243 READ\-ONLY COMPATIBLE yes 244 DEPENDENCIES none 245 .TE 246 247 This features allows ZFS to maintain more information about how free space 248 is organized within the pool. If this feature is \fBenabled\fR, ZFS will 249 set this feature to \fBactive\fR when a new space map object is created or 250 an existing space map is upgraded to the new format. Once the feature is 251 \fBactive\fR, it will remain in that state until the pool is destroyed. 252 .RE 253 254 .sp 255 .ne 2 256 .na 257 \fB\fBmulti_vdev_crash_dump\fR\fR 258 .ad 259 .RS 4n 260 .TS 261 l l . 262 GUID com.joyent:multi_vdev_crash_dump 263 READ\-ONLY COMPATIBLE no 264 DEPENDENCIES none 265 .TE 266 267 This feature allows a dump device to be configured with a pool comprised 268 of multiple vdevs. Those vdevs may be arranged in any mirrored or raidz 269 configuration. 270 271 When the \fBmulti_vdev_crash_dump\fR feature is set to \fBenabled\fR, 272 the administrator can use the \fBdumpadm\fR(1M) command to configure a 273 dump device on a pool comprised of multiple vdevs. 274 275 .SH "SEE ALSO" 276 \fBzpool\fR(1M)