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29 .Nd ZFS pool feature descriptions
31 ZFS pool on\-disk format versions are specified via "features" which replace
32 the old on\-disk format numbers (the last supported on\-disk format number is
34 To enable a feature on a pool use the
39 .Sy feature@feature_name
43 The pool format does not affect file system version compatibility or the ability
44 to send file systems between pools.
46 Since most features can be enabled independently of each other the on\-disk
47 format of the pool is specified by the set of all features marked as
49 on the pool. If the pool was created by another software version this set may
50 include unsupported features.
51 .Ss Identifying features
52 Every feature has a guid of the form
53 .Sy com.example:feature_name .
54 The reverse DNS name ensures that the feature's guid is unique across all ZFS
55 implementations. When unsupported features are encountered on a pool they will
56 be identified by their guids.
57 Refer to the documentation for the ZFS implementation that created the pool
58 for information about those features.
60 Each supported feature also has a short name.
61 By convention a feature's short name is the portion of its guid which follows
63 .Sy com.example:feature_name
64 would have the short name
66 however a feature's short name may differ across ZFS implementations if
67 following the convention would result in name conflicts.
69 Features can be in one of three states:
70 .Bl -tag -width "XXXXXXXX"
72 This feature's on\-disk format changes are in effect on the pool.
73 Support for this feature is required to import the pool in read\-write mode.
74 If this feature is not read-only compatible, support is also required to
75 import the pool in read\-only mode (see "Read\-only compatibility").
77 An administrator has marked this feature as enabled on the pool, but the
78 feature's on\-disk format changes have not been made yet.
79 The pool can still be imported by software that does not support this feature,
80 but changes may be made to the on\-disk format at any time which will move
84 Some features may support returning to the
88 See feature\-specific documentation for details.
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
94 Features cannot be disabled once they have been enabled.
97 The state of supported features is exposed through pool properties of the form
98 .Sy feature@short_name .
99 .Ss Read\-only compatibility
100 Some features may make on\-disk format changes that do not interfere with other
101 software's ability to read from the pool.
102 These features are referred to as "read\-only compatible".
103 If all unsupported features on a pool are read\-only compatible, the pool can
104 be imported in read\-only mode by setting the
106 property during import (see
108 for details on importing pools).
109 .Ss Unsupported features
110 For each unsupported feature enabled on an imported pool a pool property
112 .Sy unsupported@feature_guid
113 will indicate why the import was allowed despite the unsupported feature.
114 Possible values for this property are:
115 .Bl -tag -width "XXXXXXXX"
117 The feature is in the
119 state and therefore the pool's on\-disk format is still compatible with
120 software that does not support this feature.
122 The feature is read\-only compatible and the pool has been imported in
125 .Ss Feature dependencies
126 Some features depend on other features being enabled in order to function
128 Enabling a feature will automatically enable any features it depends on.
130 The following features are supported on this system:
131 .Bl -tag -width "XXXXXXXX"
133 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:async_destroy"
134 .It GUID Ta com.delphix:async_destroy
135 .It READ\-ONLY COMPATIBLE Ta yes
136 .It DEPENDENCIES Ta none
139 Destroying a file system requires traversing all of its data in order to
140 return its used space to the pool.
143 the file system is not fully removed until all space has been reclaimed.
144 If the destroy operation is interrupted by a reboot or power outage the next
145 attempt to open the pool will need to complete the destroy operation
150 is enabled the file system's data will be reclaimed by a background process,
151 allowing the destroy operation to complete without traversing the entire file
153 The background process is able to resume interrupted destroys after the pool
154 has been opened, eliminating the need to finish interrupted destroys as part
155 of the open operation.
156 The amount of space remaining to be reclaimed by the background process is
157 available through the
167 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:empty_bpobj"
168 .It GUID Ta com.delphix:empty_bpobj
169 .It READ\-ONLY COMPATIBLE Ta yes
170 .It DEPENDENCIES Ta none
173 This feature increases the performance of creating and using a large number
174 of snapshots of a single filesystem or volume, and also reduces the disk
177 When there are many snapshots, each snapshot uses many Block Pointer Objects
179 to track blocks associated with that snapshot.
180 However, in common use cases, most of these bpobj's are empty.
181 This feature allows us to create each bpobj on-demand, thus eliminating the
186 while there are any filesystems, volumes, or snapshots which were created
187 after enabling this feature.
192 This manual page is a
194 reimplementation of the
197 .Em zpool-features(5) ,
198 modified and customized for
200 and licensed under the Common Development and Distribution License
205 implementation of this manual page was initially written by
206 .An Martin Matuska Aq mm@FreeBSD.org .