btrfs-qgroup man page
btrfs-qgroup — control the quota group of a btrfs filesystem
btrfs qgroup <subcommand> <args>
btrfs qgroup is used to control quota group (qgroup) of a btrfs filesystem.
To use qgroup you need to enable quota first using btrfs quota enable 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 given subvolume.
The limit sare 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 automatically.
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 created again.
- 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 ancestral qgroups)
- list all qgroups which impact the given path(exclude ancestral qgroups)
- 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 qgroupid,rfer,excl,max_rfer,max_excl.
Prefix '+' means ascending order and '-' means descending order of <attr>. If no prefix is given, use ascending order by default.
If multiple <attr>s is given, use comma to separate.
btrfs qgroup returns a zero exit status if it succeeds. Non zero is returned in case of failure.
btrfs is part of btrfs-progs. Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for further details.