btrfs-qgroup(8) =============== SYNOPSIS -------- **btrfs qgroup** DESCRIPTION ----------- **btrfs qgroup** is used to control quota group (qgroup) of a btrfs filesystem. .. note:: To use qgroup you need to enable quota first using **btrfs quota enable** command. .. warning:: Qgroup is not stable yet and will impact performance in current mainline kernel (v4.14). QGROUP ------ 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 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 automatically. The qgroup hierarchy is built by commands **create** and **assign**. .. note:: If the qgroup of a subvolume is destroyed, quota about the subvolume will not be functional until qgroup *0/* is created again. SUBCOMMAND ---------- assign [options] Assign qgroup *src* as the child qgroup of *dst* in the btrfs filesystem identified by *path*. ``Options`` --rescan (default since: 4.19) Automatically schedule quota rescan if the new qgroup assignment would lead to quota inconsistency. See *QUOTA RESCAN* for more information. --no-rescan Explicitly ask not to do a rescan, even if the assignment will make the quotas inconsistent. This may be useful for repeated calls where the rescan would add unnecessary overhead. create Create a subvolume quota group. For the *0/* qgroup, a qgroup can be created even before the subvolume is created. destroy Destroy a qgroup. If a qgroup is not isolated, meaning it is a parent or child qgroup, then it can only be destroyed after the relationship is removed. limit [options] |none [] 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. ``Options`` -c limit amount of data after compression. This is the default, it is currently not possible to turn off this option. -e limit space exclusively assigned to this qgroup. remove Remove the relationship between child qgroup *src* and parent qgroup *dst* in the btrfs filesystem identified by *path*. ``Options`` --rescan (default since: 4.19) Automatically schedule quota rescan if the removed qgroup relation would lead to quota inconsistency. See *QUOTA RESCAN* for more information. --no-rescan Explicitly ask not to do a rescan, even if the removal will make the quotas inconsistent. This may be useful for repeated calls where the rescan would add unnecessary overhead. show [options] Show all qgroups in the btrfs filesystem identified by . ``Options`` -p print parent qgroup id. -c print child qgroup id. -r print limit of referenced size of qgroup. -e print limit of exclusive size of qgroup. -F list all qgroups which impact the given path(include ancestral qgroups) -f list all qgroups which impact the given path(exclude ancestral qgroups) --raw raw numbers in bytes, without the *B* suffix. --human-readable print human friendly numbers, base 1024, this is the default --iec select the 1024 base for the following options, according to the IEC standard. --si select the 1000 base for the following options, according to the SI standard. --kbytes show sizes in KiB, or kB with --si. --mbytes show sizes in MiB, or MB with --si. --gbytes show sizes in GiB, or GB with --si. --tbytes show sizes in TiB, or TB with --si. --sort=[\+/-][,[+/-]]... list qgroups in order of . 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* values are given, use comma to separate. --sync To retrieve information after updating the state of qgroups, force sync of the filesystem identified by *path* before getting information. QUOTA RESCAN ------------ The rescan reads all extent sharing metadata and updates the respective qgoups accordingly. The information consists of bytes owned exclusively (*excl*) or shared/referred to (*rfer*). There's no explicit information about which extents are shared or owned exclusively. This means when qgroup relationship changes, extent owners change and qgroup numbers are no longer consistent unless we do a full rescan. However there are cases where we can avoid a full rescan, if a subvolume whose *rfer* number equals its *excl* number, which means all bytes are exclusively owned, then assigning/removing this subvolume only needs to add/subtract *rfer* number from its parent qgroup. This can speed up the rescan. EXAMPLES -------- Make a parent group that has two quota group children ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Given the following filesystem mounted at `/mnt/my-vault` .. code-block:: none Label: none uuid: 60d2ab3b-941a-4f22-8d1a-315f329797b2 Total devices 1 FS bytes used 128.00KiB devid 1 size 5.00GiB used 536.00MiB path /dev/vdb Enable quota and create subvolumes. Check subvolume ids. .. code-block:: bash $ cd /mnt/my-vault $ btrfs quota enable . $ btrfs subvolume create a $ btrfs subvolume create b $ btrfs subvolume list . ID 261 gen 61 top level 5 path a ID 262 gen 62 top level 5 path b Create qgroup and set limit to 10MiB. .. code-block:: bash $ btrfs qgroup create 1/100 . $ btrfs qgroup limit 10M 1/100 . $ btrfs qgroup assign 0/261 1/100 . $ btrfs qgroup assign 0/262 1/100 . And check qgroups. .. code-block:: bash $ btrfs qgroup show . qgroupid rfer excl -------- ---- ---- 0/5 16.00KiB 16.00KiB 0/261 16.00KiB 16.00KiB 0/262 16.00KiB 16.00KiB 1/100 32.00KiB 32.00KiB EXIT STATUS ----------- **btrfs qgroup** returns a zero exit status if it succeeds. Non zero is returned in case of failure. AVAILABILITY ------------ **btrfs** is part of btrfs-progs. Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for further details. SEE ALSO -------- ``mkfs.btrfs(8)``, ``btrfs-subvolume(8)``, ``btrfs-quota(8)``,