1 '\" te 2 .\" Copyright (c) 2012 by Delphix. All rights reserved. 3 .\" Copyright (c) 2012 Joyent, Inc. All rights reserved. 4 .\" The contents of this file are subject to the terms of the Common Development 5 .\" and Distribution License (the "License"). You may not use this file except 6 .\" in compliance with the License. You can obtain a copy of the license at 7 .\" usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing. 8 .\" 9 .\" See the License for the specific language governing permissions and 10 .\" limitations under the License. When distributing Covered Code, include this 11 .\" CDDL HEADER in each file and include the License file at 12 .\" usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this 13 .\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your 14 .\" own identifying information: 15 .\" Portions Copyright [yyyy] [name of copyright owner] 16 .TH ZPOOL-FEATURES 5 "Oct 24, 2012" 17 .SH NAME 18 zpool\-features \- ZFS pool feature descriptions 19 .SH DESCRIPTION 20 .sp 21 .LP 22 ZFS pool on\-disk format versions are specified via "features" which replace 23 the old on\-disk format numbers (the last supported on\-disk format number is 24 28). To enable a feature on a pool use the \fBupgrade\fR subcommand of the 25 \fBzpool\fR(1M) command, or set the \fBfeature@\fR\fIfeature_name\fR property 26 to \fBenabled\fR. 27 .sp 28 .LP 29 The pool format does not affect file system version compatibility or the ability 30 to send file systems between pools. 31 .sp 32 .LP 33 Since most features can be enabled independently of each other the on\-disk 34 format of the pool is specified by the set of all features marked as 35 \fBactive\fR on the pool. If the pool was created by another software version 36 this set may include unsupported features. 37 .SS "Identifying features" 38 .sp 39 .LP 40 Every feature has a guid of the form \fIcom.example:feature_name\fR. The reverse 41 DNS name ensures that the feature's guid is unique across all ZFS 42 implementations. When unsupported features are encountered on a pool they will 43 be identified by their guids. Refer to the documentation for the ZFS 44 implementation that created the pool for information about those features. 45 .sp 46 .LP 47 Each supported feature also has a short name. By convention a feature's short 48 name is the portion of its guid which follows the ':' (e.g. 49 \fIcom.example:feature_name\fR would have the short name \fIfeature_name\fR), 50 however a feature's short name may differ across ZFS implementations if 51 following the convention would result in name conflicts. 52 .SS "Feature states" 53 .sp 54 .LP 55 Features can be in one of three states: 56 .sp 57 .ne 2 58 .na 59 \fB\fBactive\fR\fR 60 .ad 61 .RS 12n 62 This feature's on\-disk format changes are in effect on the pool. Support for 63 this feature is required to import the pool in read\-write mode. If this 64 feature is not read-only compatible, support is also required to import the pool 65 in read\-only mode (see "Read\-only compatibility"). 66 .RE 67 68 .sp 69 .ne 2 70 .na 71 \fB\fBenabled\fR\fR 72 .ad 73 .RS 12n 74 An administrator has marked this feature as enabled on the pool, but the 75 feature's on\-disk format changes have not been made yet. The pool can still be 76 imported by software that does not support this feature, but changes may be made 77 to the on\-disk format at any time which will move the feature to the 78 \fBactive\fR state. Some features may support returning to the \fBenabled\fR 79 state after becoming \fBactive\fR. See feature\-specific documentation for 80 details. 81 .RE 82 83 .sp 84 .ne 2 85 .na 86 \fBdisabled\fR 87 .ad 88 .RS 12n 89 This feature's on\-disk format changes have not been made and will not be made 90 unless an administrator moves the feature to the \fBenabled\fR state. Features 91 cannot be disabled once they have been enabled. 92 .RE 93 94 .sp 95 .LP 96 The state of supported features is exposed through pool properties of the form 97 \fIfeature@short_name\fR. 98 .SS "Read\-only compatibility" 99 .sp 100 .LP 101 Some features may make on\-disk format changes that do not interfere with other 102 software's ability to read from the pool. These features are referred to as 103 "read\-only compatible". If all unsupported features on a pool are read\-only 104 compatible, the pool can be imported in read\-only mode by setting the 105 \fBreadonly\fR property during import (see \fBzpool\fR(1M) for details on 106 importing pools). 107 .SS "Unsupported features" 108 .sp 109 .LP 110 For each unsupported feature enabled on an imported pool a pool property 111 named \fIunsupported@feature_guid\fR will indicate why the import was allowed 112 despite the unsupported feature. Possible values for this property are: 113 114 .sp 115 .ne 2 116 .na 117 \fB\fBinactive\fR\fR 118 .ad 119 .RS 12n 120 The feature is in the \fBenabled\fR state and therefore the pool's on\-disk 121 format is still compatible with software that does not support this feature. 122 .RE 123 124 .sp 125 .ne 2 126 .na 127 \fB\fBreadonly\fR\fR 128 .ad 129 .RS 12n 130 The feature is read\-only compatible and the pool has been imported in 131 read\-only mode. 132 .RE 133 134 .SS "Feature dependencies" 135 .sp 136 .LP 137 Some features depend on other features being enabled in order to function 138 properly. Enabling a feature will automatically enable any features it 139 depends on. 140 .SH FEATURES 141 .sp 142 .LP 143 The following features are supported on this system: 144 .sp 145 .ne 2 146 .na 147 \fB\fBasync_destroy\fR\fR 148 .ad 149 .RS 4n 150 .TS 151 l l . 152 GUID com.delphix:async_destroy 153 READ\-ONLY COMPATIBLE yes 154 DEPENDENCIES none 155 .TE 156 157 Destroying a file system requires traversing all of its data in order to 158 return its used space to the pool. Without \fBasync_destroy\fR the file system 159 is not fully removed until all space has been reclaimed. If the destroy 160 operation is interrupted by a reboot or power outage the next attempt to open 161 the pool will need to complete the destroy operation synchronously. 162 163 When \fBasync_destroy\fR is enabled the file system's data will be reclaimed 164 by a background process, allowing the destroy operation to complete without 165 traversing the entire file system. The background process is able to resume 166 interrupted destroys after the pool has been opened, eliminating the need 167 to finish interrupted destroys as part of the open operation. The amount 168 of space remaining to be reclaimed by the background process is available 169 through the \fBfreeing\fR property. 170 171 This feature is only \fBactive\fR while \fBfreeing\fR is non\-zero. 172 .RE 173 174 .sp 175 .ne 2 176 .na 177 \fB\fBempty_bpobj\fR\fR 178 .ad 179 .RS 4n 180 .TS 181 l l . 182 GUID com.delphix:empty_bpobj 183 READ\-ONLY COMPATIBLE yes 184 DEPENDENCIES none 185 .TE 186 187 This feature increases the performance of creating and using a large 188 number of snapshots of a single filesystem or volume, and also reduces 189 the disk space required. 190 191 When there are many snapshots, each snapshot uses many Block Pointer 192 Objects (bpobj's) to track blocks associated with that snapshot. 193 However, in common use cases, most of these bpobj's are empty. This 194 feature allows us to create each bpobj on-demand, thus eliminating the 195 empty bpobjs. 196 197 This feature is \fBactive\fR while there are any filesystems, volumes, 198 or snapshots which were created after enabling this feature. 199 .RE 200 201 .sp 202 .ne 2 203 .na 204 \fB\fBfilesystem_limits\fR\fR 205 .ad 206 .RS 4n 207 .TS 208 l l . 209 GUID com.joyent:filesystem_limits 210 READ\-ONLY COMPATIBLE yes 211 DEPENDENCIES none 212 .TE 213 214 This feature enables filesystem and snapshot limits. These limits can be used 215 to control how many filesystems and/or snapshots can be created at the point in 216 the tree on which the limits are set. 217 218 This feature is \fBactive\fR once either of the limit properties has been 219 set on a dataset and is deactivated when the last limit is removed. 220 .RE 221 222 .SH "SEE ALSO" 223 \fBzpool\fR(1M)