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