btrfs qgroup is used to control quota group (qgroup) of a btrfs
To use qgroup you need to enable quota first using btrfs quotaenable command.
Qgroup is not stable yet and will impact performance in current
mainline kernel (v3.14 so far).
Quota groups or qgroup in btrfs make a tree hierarchy, the leaf
qgroups are attached to subvolumes. The size limits are set per
qgroup and apply when any limit is reached in tree that contains a
The limits are separated between shared and exclusive and reflect the
extent ownership. For example a fresh snapshot shares almost all the
blocks with the original subvolume, new writes to either subvolume
will raise towards the exclusive limit.
The qgroup identifiers conform to level/id where level 0 is reserved
to the qgroups associated with subvolumes. Such qgroups are created
The qgroup hierarchy is built by commands create and assign.
If the qgroup of a subvolume is destroyed, quota about the
subvolume will not be functional until qgroup 0/<subvolume id> is
assign [options] <src> <dst> <path>
Assign qgroup <src> as the child qgroup of <dst> in the btrfs
filesystem identified by <path>.
Automatically schedule quota rescan if the new qgroup
assignment leads to quota inconsistency.
Explicitly ask not to do a rescan.
create <qgroupid> <path>
Create a subvolume quota group.
For the 0/<subvolume id> qgroup, a qgroup can be created even
before the subvolume created.
destroy <qgroupid> <path>
Destroy a qgroup.
If a qgroup is no isolated,which means it is a parent or child
qgroup, it can’t be destroyed.
limit [options] <size>|none [<qgroupid>] <path>
Limit the size of a qgroup to <size> or no limit in the btrfs
filesystem identified by <path>.
If <qgroupid> is not given, qgroup of the subvolume identified by
<path> is used if possible.
limit amount of data after compression. This is the default,
it is currently not possible to turn off this option.
limit space exclusively assigned to this qgroup.
remove <src> <dst> <path>
Remove the relationship between child qgroup <src> and parent
qgroup <dst> in the btrfs filesystem identified by <path>.
show [options] <path>
Show all qgroups in the btrfs filesystem identified by <path>.
print parent qgroup id.
print child qgroup id.
print limit of referenced size of qgroup.
print limit of exclusive size of qgroup.
list all qgroups which impact the given path(include
list all qgroups which impact the given path(exclude
raw numbers in bytes, without the B suffix.
print human friendly numbers, base 1024, this is the default
select the 1024 base for the following options, according to
the IEC standard.
select the 1000 base for the following options, according to
the SI standard.
show sizes in KiB, or kB with --si.
show sizes in MiB, or MB with --si.
show sizes in GiB, or GB with --si.
show sizes in TiB, or TB with --si.
list qgroups in order of <attr>.
<attr> can be one or more of
Prefix '+' means ascending order and '-' means descending
order of <attr>. If no prefix is given, use ascending order
If multiple <attr>s is given, use comma to separate.
To retrieve information after updating the state of qgroups,
force sync of the filesystem identified by <path> before
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Btrfs v4.6.1 02/18/2017 BTRFS-QGROUP(8)