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home | helpx minix x x minixx BTRFS-QGROUP(8) Btrfs Manual BTRFS-QGROUP(8) NAME btrfs-qgroup - control the quota group of a btrfs filesystem SYNOPSIS btrfs qgroup _subcommand_ _args_ 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/_subvolume id_ is created again. SUBCOMMAND assign [options] _src_ _dst_ _path_ 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 _qgroupid_ _path_ Create a subvolume quota group. For the 0/_subvolume id_ qgroup, a qgroup can be created even before the subvolume is created. destroy _qgroupid_ _path_ 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] _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. 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 _src_ _dst_ _path_ Remove the relationship between child qgroup _src_ and parent qgroup _dst_ in the btrfs filesystem identified by _path_. Options The same as assign subcommand. show [options] _path_ Show all qgroups in the btrfs filesystem identified by _path_. 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=[+/-]_attr_[,[+/-]_attr_]... 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. --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. 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), Btrfs v5.4.1 01/09/2020 BTRFS-QGROUP(8)
NAME | SYNOPSIS | DESCRIPTION | QGROUP | SUBCOMMAND | QUOTA RESCAN | EXIT STATUS | AVAILABILITY | SEE ALSO