1BTRFS-QGROUP(8) BTRFS BTRFS-QGROUP(8)
2
6 btrfs-qgroup - control the quota group of a btrfs filesystem
7
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 en‐
17 able 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 ap‐
26 ply when any limit is reached in tree that contains a given subvolume.
27 The limits are separated between shared and exclusive and reflect the
29 extent ownership. For example a fresh snapshot shares almost all the
30 blocks with the original subvolume, new writes to either subvolume will
31 raise towards the exclusive limit.
32 The qgroup identifiers conform to level/id where level 0 is reserved to
34 the qgroups associated with subvolumes. Such qgroups are created auto‐
35 matically.
36 The qgroup hierarchy is built by commands create and assign.
38 NOTE:
40 If the qgroup of a subvolume is destroyed, quota about the subvolume
41 will not be functional until qgroup 0/<subvolume id> is created
42 again.
43
45 assign [options] <src> <dst> <path>
46 Assign qgroup src as the child qgroup of dst in the btrfs
47 filesystem identified by path.
48 Options
50 --rescan
52 (default since: 4.19) Automatically schedule quota rescan
53 if the new qgroup assignment would lead to quota incon‐
54 sistency. See QUOTA RESCAN for more information.
55 --no-rescan
57 Explicitly ask not to do a rescan, even if the assignment
58 will make the quotas inconsistent. This may be useful for
59 repeated calls where the rescan would add unnecessary
60 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 limit amount of data after compression. This is the de‐
85 fault, it is currently not possible to turn off this op‐
86 tion.
87 -e limit space exclusively assigned to this qgroup.
89 remove <src> <dst> <path>
91 Remove the relationship between child qgroup src and parent
92 qgroup dst in the btrfs filesystem identified by path.
93 Options
95 --rescan
97 (default since: 4.19) Automatically schedule quota rescan
98 if the removed qgroup relation would lead to quota incon‐
99 sistency. See QUOTA RESCAN for more information.
100 --no-rescan
102 Explicitly ask not to do a rescan, even if the removal
103 will make the quotas inconsistent. This may be useful for
104 repeated calls where the rescan would add unnecessary
105 overhead.
106 show [options] <path>
108 Show all qgroups in the btrfs filesystem identified by <path>.
109 Options
111 -p print parent qgroup id.
113 -c print child qgroup id.
115 -r print limit of referenced size of qgroup.
117 -e print limit of exclusive size of qgroup.
119 -F list all qgroups which impact the given path(include an‐
121 cestral qgroups)
122 -f list all qgroups which impact the given path(exclude an‐
124 cestral qgroups)
125 --raw raw numbers in bytes, without the B suffix.
127 --human-readable
129 print human friendly numbers, base 1024, this is the de‐
130 fault
131 --iec select the 1024 base for the following options, according
133 to the IEC standard.
134 --si select the 1000 base for the following options, according
136 to 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 or‐
157 der of attr. If no prefix is given, use ascending order
158 by default.
159 If multiple attr values are given, use comma to separate.
161 --sync To retrieve information after updating the state of
163 qgroups, force sync of the filesystem identified by path
164 before getting information.
165
167 The rescan reads all extent sharing metadata and updates the respective
168 qgoups accordingly.
169 The information consists of bytes owned exclusively (excl) or
171 shared/referred to (rfer). There's no explicit information about which
172 extents are shared or owned exclusively. This means when qgroup rela‐
173 tionship changes, extent owners change and qgroup numbers are no longer
174 consistent unless we do a full rescan.
175 However there are cases where we can avoid a full rescan, if a subvol‐
177 ume whose rfer number equals its excl number, which means all bytes are
178 exclusively owned, then assigning/removing this subvolume only needs to
179 add/subtract rfer number from its parent qgroup. This can speed up the
180 rescan.
181
183 Make a parent group that has two quota group children
184 Given the following filesystem mounted at /mnt/my-vault
185 Label: none uuid: 60d2ab3b-941a-4f22-8d1a-315f329797b2
187 Total devices 1 FS bytes used 128.00KiB
188 devid 1 size 5.00GiB used 536.00MiB path /dev/vdb
189 Enable quota and create subvolumes. Check subvolume ids.
191 $ cd /mnt/my-vault
193 $ btrfs quota enable .
194 $ btrfs subvolume create a
195 $ btrfs subvolume create b
196 $ btrfs subvolume list .
197 ID 261 gen 61 top level 5 path a
199 ID 262 gen 62 top level 5 path b
200 Create qgroup and set limit to 10MiB.
202 $ btrfs qgroup create 1/100 .
204 $ btrfs qgroup limit 10M 1/100 .
205 $ btrfs qgroup assign 0/261 1/100 .
206 $ btrfs qgroup assign 0/262 1/100 .
207 And check qgroups.
209 $ btrfs qgroup show .
211 qgroupid rfer excl
213 -------- ---- ----
214 0/5 16.00KiB 16.00KiB
215 0/261 16.00KiB 16.00KiB
216 0/262 16.00KiB 16.00KiB
217 1/100 32.00KiB 32.00KiB
218
220 btrfs qgroup returns a zero exit status if it succeeds. Non zero is re‐
221 turned in case of failure.
222
224 btrfs is part of btrfs-progs. Please refer to the btrfs wiki
225 http://btrfs.wiki.kernel.org for further details.
226
228 mkfs.btrfs(8), btrfs-subvolume(8), btrfs-quota(8),
229
231 2022
2325.18 May 25, 2022 BTRFS-QGROUP(8)