1BTRFS-QGROUP(8) Btrfs Manual BTRFS-QGROUP(8)
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6 btrfs-qgroup - control the quota group of a btrfs filesystem
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9 btrfs qgroup <subcommand> <args>
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12 btrfs qgroup is used to control quota group (qgroup) of a btrfs
13 filesystem.
14 Note
16 To use qgroup you need to enable quota first using btrfs quota
17 enable command.
18 Warning
20 Qgroup is not stable yet and will impact performance in current
21 mainline kernel (v4.14).
22
24 Quota groups or qgroup in btrfs make a tree hierarchy, the leaf qgroups
25 are attached to subvolumes. The size limits are set per qgroup and
26 apply when any limit is reached in tree that contains a given
27 subvolume.
28 The limits are separated between shared and exclusive and reflect the
30 extent ownership. For example a fresh snapshot shares almost all the
31 blocks with the original subvolume, new writes to either subvolume will
32 raise towards the exclusive limit.
33 The qgroup identifiers conform to level/id where level 0 is reserved to
35 the qgroups associated with subvolumes. Such qgroups are created
36 automatically.
37 The qgroup hierarchy is built by commands create and assign.
39 Note
41 If the qgroup of a subvolume is destroyed, quota about the
42 subvolume will not be functional until qgroup 0/<subvolume id> is
43 created again.
44
46 assign [options] <src> <dst> <path>
47 Assign qgroup <src> as the child qgroup of <dst> in the btrfs
48 filesystem identified by <path>.
49 Options
51 --rescan
53 (default since: 4.19) Automatically schedule quota rescan if
54 the new qgroup assignment would lead to quota inconsistency.
55 See QUOTA RESCAN for more information.
56 --no-rescan
58 Explicitly ask not to do a rescan, even if the assignment will
59 make the quotas inconsistent. This may be useful for repeated
60 calls where the rescan would add unnecessary overhead.
61 create <qgroupid> <path>
63 Create a subvolume quota group.
64 For the 0/<subvolume id> qgroup, a qgroup can be created even
66 before the subvolume is created.
67 destroy <qgroupid> <path>
69 Destroy a qgroup.
70 If a qgroup is not isolated, meaning it is a parent or child
72 qgroup, then it can only be destroyed after the relationship is
73 removed.
74 limit [options] <size>|none [<qgroupid>] <path>
76 Limit the size of a qgroup to <size> or no limit in the btrfs
77 filesystem identified by <path>.
78 If <qgroupid> is not given, qgroup of the subvolume identified by
80 <path> is used if possible.
81 Options
83 -c
85 limit amount of data after compression. This is the default, it
86 is currently not possible to turn off this option.
87 -e
89 limit space exclusively assigned to this qgroup.
90 remove <src> <dst> <path>
92 Remove the relationship between child qgroup <src> and parent
93 qgroup <dst> in the btrfs filesystem identified by <path>.
94 Options
96 The same as assign subcommand.
98 show [options] <path>
100 Show all qgroups in the btrfs filesystem identified by <path>.
101 Options
103 -p
105 print parent qgroup id.
106 -c
108 print child qgroup id.
109 -r
111 print limit of referenced size of qgroup.
112 -e
114 print limit of exclusive size of qgroup.
115 -F
117 list all qgroups which impact the given path(include ancestral
118 qgroups)
119 -f
121 list all qgroups which impact the given path(exclude ancestral
122 qgroups)
123 --raw
125 raw numbers in bytes, without the B suffix.
126 --human-readable
128 print human friendly numbers, base 1024, this is the default
129 --iec
131 select the 1024 base for the following options, according to
132 the IEC standard.
133 --si
135 select the 1000 base for the following options, according to
136 the SI standard.
137 --kbytes
139 show sizes in KiB, or kB with --si.
140 --mbytes
142 show sizes in MiB, or MB with --si.
143 --gbytes
145 show sizes in GiB, or GB with --si.
146 --tbytes
148 show sizes in TiB, or TB with --si.
149 --sort=[+/-]<attr>[,[+/-]<attr>]...
151 list qgroups in order of <attr>.
152 <attr> can be one or more of
154 qgroupid,rfer,excl,max_rfer,max_excl.
155 Prefix '+' means ascending order and '-' means descending order
157 of <attr>. If no prefix is given, use ascending order by
158 default.
159 If multiple <attr>s is given, use comma to separate.
161 --sync
163 To retrieve information after updating the state of qgroups,
164 force sync of the filesystem identified by <path> before
165 getting information.
166
168 The rescan reads all extent sharing metadata and updates the respective
169 qgoups accordingly.
170 The information consists of bytes owned exclusively (excl) or
172 shared/referred to (rfer). There’s no explicit information about which
173 extents are shared or owned exclusively. This means when qgroup
174 relationship changes, extent owners change and qgroup numbers are no
175 longer consistent unless we do a full rescan.
176 However there are cases where we can avoid a full rescan, if a
178 subvolume whose rfer number equals its excl number, which means all
179 bytes are exclusively owned, then assigning/removing this subvolume
180 only needs to add/subtract rfer number from its parent qgroup. This can
181 speed up the rescan.
182
184 btrfs qgroup returns a zero exit status if it succeeds. Non zero is
185 returned in case of failure.
186
188 btrfs is part of btrfs-progs. Please refer to the btrfs wiki
189 http://btrfs.wiki.kernel.org for further details.
190
192 mkfs.btrfs(8), btrfs-subvolume(8), btrfs-quota(8),
193Btrfs v5.4 12/03/2019 BTRFS-QGROUP(8)