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  16 .TH ZPOOL-FEATURES 5 "Oct 24, 2012"
  17 .SH NAME
  18 zpool\-features \- ZFS pool feature descriptions
  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
  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
  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
  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:
 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
 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
 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.
 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
 154 DEPENDENCIES    none
 155 .TE
 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.
 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.
 171 This feature is only \fBactive\fR while \fBfreeing\fR is non\-zero.
 172 .RE
 174 .sp
 175 .ne 2
 176 .na
 177 \fB\fBdataset_quota\fR\fR
 178 .ad
 179 .RS 4n
 180 .TS
 181 l l .
 182 GUID    com.joyent:dataset_quota
 184 DEPENDENCIES    none
 185 .TE
 187 This feature enables dataset quotas and snapshot quotas. These quotas
 188 can be used to limit how many datasets and/or snapshots can be created
 189 under the dataset on which the quotas are set.
 191 This feature is \fBactive\fR once either of the quota properties has been
 192 set on a dataset.
 193 .RE
 195 .sp
 196 .ne 2
 197 .na
 198 \fB\fBempty_bpobj\fR\fR
 199 .ad
 200 .RS 4n
 201 .TS
 202 l l .
 203 GUID    com.delphix:empty_bpobj
 205 DEPENDENCIES    none
 206 .TE
 208 This feature increases the performance of creating and using a large
 209 number of snapshots of a single filesystem or volume, and also reduces
 210 the disk space required.
 212 When there are many snapshots, each snapshot uses many Block Pointer
 213 Objects (bpobj's) to track blocks associated with that snapshot.
 214 However, in common use cases, most of these bpobj's are empty.  This
 215 feature allows us to create each bpobj on-demand, thus eliminating the
 216 empty bpobjs.
 218 This feature is \fBactive\fR while there are any filesystems, volumes,
 219 or snapshots which were created after enabling this feature.
 220 .RE
 222 .SH "SEE ALSO"
 223 \fBzpool\fR(1M)