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>
10
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 --rescan
98 (default since: 4.19) Automatically schedule quota rescan if
99 the removed qgroup relation would lead to quota inconsistency.
100 See QUOTA RESCAN for more information.
101 --no-rescan
103 Explicitly ask not to do a rescan, even if the removal will
104 make the quotas inconsistent. This may be useful for repeated
105 calls where the rescan would add unnecessary overhead.
106 show [options] <path>
108 Show all qgroups in the btrfs filesystem identified by <path>.
109 Options
111 -p
113 print parent qgroup id.
114 -c
116 print child qgroup id.
117 -r
119 print limit of referenced size of qgroup.
120 -e
122 print limit of exclusive size of qgroup.
123 -F
125 list all qgroups which impact the given path(include ancestral
126 qgroups)
127 -f
129 list all qgroups which impact the given path(exclude ancestral
130 qgroups)
131 --raw
133 raw numbers in bytes, without the B suffix.
134 --human-readable
136 print human friendly numbers, base 1024, this is the default
137 --iec
139 select the 1024 base for the following options, according to
140 the IEC standard.
141 --si
143 select the 1000 base for the following options, according to
144 the SI standard.
145 --kbytes
147 show sizes in KiB, or kB with --si.
148 --mbytes
150 show sizes in MiB, or MB with --si.
151 --gbytes
153 show sizes in GiB, or GB with --si.
154 --tbytes
156 show sizes in TiB, or TB with --si.
157 --sort=[+/-]<attr>[,[+/-]<attr>]...
159 list qgroups in order of <attr>.
160 <attr> can be one or more of
162 qgroupid,rfer,excl,max_rfer,max_excl.
163 Prefix '+' means ascending order and '-' means descending order
165 of <attr>. If no prefix is given, use ascending order by
166 default.
167 If multiple <attr>s is given, use comma to separate.
169 --sync
171 To retrieve information after updating the state of qgroups,
172 force sync of the filesystem identified by <path> before
173 getting information.
174
176 The rescan reads all extent sharing metadata and updates the respective
177 qgoups accordingly.
178 The information consists of bytes owned exclusively (excl) or
180 shared/referred to (rfer). There’s no explicit information about which
181 extents are shared or owned exclusively. This means when qgroup
182 relationship changes, extent owners change and qgroup numbers are no
183 longer consistent unless we do a full rescan.
184 However there are cases where we can avoid a full rescan, if a
186 subvolume whose rfer number equals its excl number, which means all
187 bytes are exclusively owned, then assigning/removing this subvolume
188 only needs to add/subtract rfer number from its parent qgroup. This can
189 speed up the rescan.
190
192 Example 1. Make a parent group that has two quota group children
193 Given the following filesystem mounted at /mnt/my-vault
195 Label: none uuid: 60d2ab3b-941a-4f22-8d1a-315f329797b2
197 Total devices 1 FS bytes used 128.00KiB
198 devid 1 size 5.00GiB used 536.00MiB path /dev/vdb
199 Enable quota and create subvolumes. Check subvolume ids.
201 $ cd /mnt/my-vault
203 $ btrfs quota enable .
204 $ btrfs subvolume create a
205 $ btrfs subvolume create b
206 $ btrfs subvolume list .
207 ID 261 gen 61 top level 5 path a
209 ID 262 gen 62 top level 5 path b
210 Create qgroup and set limit to 10MiB.
212 $ btrfs qgroup create 1/100 .
214 $ btrfs qgroup limit 10M 1/100 .
215 $ btrfs qgroup assign 0/261 1/100 .
216 $ btrfs qgroup assign 0/262 1/100 .
217 And check qgroups.
219 $ btrfs qgroup show .
221 qgroupid rfer excl
223 -------- ---- ----
224 0/5 16.00KiB 16.00KiB
225 0/261 16.00KiB 16.00KiB
226 0/262 16.00KiB 16.00KiB
227 1/100 32.00KiB 32.00KiB
228
230 btrfs qgroup returns a zero exit status if it succeeds. Non zero is
231 returned in case of failure.
232
234 btrfs is part of btrfs-progs. Please refer to the btrfs wiki
235 http://btrfs.wiki.kernel.org for further details.
236
238 mkfs.btrfs(8), btrfs-subvolume(8), btrfs-quota(8),
239Btrfs v5.10 01/18/2021 BTRFS-QGROUP(8)