An example with description:
$ btrfs filesystem df /path Data, single: total=1.15TiB, used=1.13TiB System, single: total=32.00MiB, used=144.00KiB Metadata, single: total=12.00GiB, used=6.45GiB GlobalReserve, single: total=512.00MiB, used=0.00B
GlobalReserve is an artificial and internal emergency space. It is used eg. when the filesystem is full. Its total size is dynamic based on the filesystem size, usually not larger than 512MiB, used may fluctuate.
The GlobalReserve is a portion of Metadata. In case the filesystem metadata is exhausted, GlobalReserve/total + Metadata/used = Metadata/total. Otherwise there appears to be some unused space of Metadata.
If conflicting options are passed, the last one takes precedence.
defragment [options] <file>|<dir> [<file>|<dir>...]
If -r is passed, files in dir will be defragmented recursively (not descending to subvolumes, mount points and directory symlinks). The start position and the number of bytes to defragment can be specified by start and length using -s and -l options below. Extents bigger than value given by -t will be skipped, otherwise this value is used as a target extent size, but is only advisory and may not be reached if the free space is too fragmented. Use 0 to take the kernel default, which is 256kB but may change in the future. You can also turn on compression in defragment operations.
Defragmenting with Linux kernel versions < 3.9 or ≥ 3.14-rc2 as well as with Linux stable kernel versions ≥ 3.10.31, ≥ 3.12.12 or ≥ 3.13.4 will break up the reflinks of COW data (for example files copied with cp --reflink, snapshots or de-duplicated data). This may cause considerable increase of space usage depending on the broken up reflinks.
Directory arguments without -r do not defragment files recursively but will defragment certain internal trees (extent tree and the subvolume tree). This has been confusing and could be removed in the future.
This will limit the amount of dirty data to current file, otherwise the amount accumulates from several files and will increase system load. This can also lead to ENOSPC if there’s too much dirty data to write and it’s not possible to make the reservations for the new data (ie. how the COW design works).
The value is only advisory and the final size of the extents may differ, depending on the state of the free space and fragmentation or other internal logic. Reasonable values are from tens to hundreds of megabytes.
du [options] <path> [<path>..]
Each argument to btrfs filesystem du will have a set shared value calculated for it. We define each set as those files found by a recursive search of an argument (recursion descends to subvolumes but not mount points). The set shared value then is a sum of all shared space referenced by the set.
set shared takes into account overlapping shared extents, hence it isn’t as simple as adding up shared extents.
label [<device>|<mountpoint>] [<newlabel>]
The newlabel argument is optional. Current label is printed if the argument is omitted.
the maximum allowable length shall be less than 256 chars and must not contain a newline. The trailing newline is stripped automatically.
resize [options] [<devid>:][+/-]<size>[kKmMgGtTpPeE]|[<devid>:]max <path>
If path is a file containing a BTRFS image then resize does not work as expected and does not resize the image. This would resize the underlying filesystem instead.
If max is passed, the filesystem will occupy all available space on the device respecting devid (remember, devid 1 by default).
The resize command does not manipulate the size of underlying partition. If you wish to enlarge/reduce a filesystem, you must make sure you can expand the partition before enlarging the filesystem and shrink the partition after reducing the size of the filesystem. This can done using fdisk(8) or parted(8) to delete the existing partition and recreate it with the new desired size. When recreating the partition make sure to use the same starting partition offset as before.
Growing is usually instant as it only updates the size. However, shrinking could take a long time if there are data in the device area that’s beyond the new end. Relocation of the data takes time.
See also section EXAMPLES.
show [options] [<path>|<uuid>|<device>|<label>]
If no option none of path/uuid/device/label is passed, information about all the BTRFS filesystems is shown, both mounted and unmounted.
usage [options] <path> [<path>...]
The level of detail can differ if the command is run under a regular or the root user (due to use of restricted ioctl). For both there’s a summary section with information about space usage:
$ btrfs filesystem usage /path WARNING: cannot read detailed chunk info, RAID5/6 numbers will be incorrect, run as root Overall: Device size: 1.82TiB Device allocated: 1.17TiB Device unallocated: 669.99GiB Device missing: 0.00B Used: 1.14TiB Free (estimated): 692.57GiB (min: 692.57GiB) Free (statfs, df) 692.57GiB Data ratio: 1.00 Metadata ratio: 1.00 Global reserve: 512.00MiB (used: 0.00B) Multiple profiles: no
The root user will also see stats broken down by block group types:
Data,single: Size:1.15TiB, Used:1.13TiB (98.26%) /dev/sdb 1.15TiB Metadata,single: Size:12.00GiB, Used:6.45GiB (53.75%) /dev/sdb 12.00GiB System,single: Size:32.00MiB, Used:144.00KiB (0.44%) /dev/sdb 32.00MiB Unallocated: /dev/sdb 669.99GiB
Data is block group type, single is block group profile, Size is total size occupied by this type, Used is the actually used space, the percent is ratio of Used/Size. The Unallocated is remaining space.
If conflicting options are passed, the last one takes precedence.
Recursively defragment files under dir/, print files as they are processed. The file names will be printed in batches, similarly the amount of data triggered by defragmentation will be proportional to last N printed files. The system dirty memory throttling will slow down the defragmentation but there can still be a lot of IO load and the system may stall for a moment.
$ btrfs filesystem defrag -v -r -f dir/
Recursively defragment files under dir/, be verbose and wait until all blocks are flushed before processing next file. You can note slower progress of the output and lower IO load (proportional to currently defragmented file).
$ btrfs filesystem defrag -v -r -f -clzo dir/
Recursively defragment files under dir/, be verbose, wait until all blocks are flushed and force file compression.
$ btrfs filesystem defrag -v -r -t 64M dir/
Recursively defragment files under dir/, be verbose and try to merge extents to be about 64MiB. As stated above, the success rate depends on actual free space fragmentation and the final result is not guaranteed to meet the target even if run repeatedly.
$ btrfs filesystem resize -1G /path
$ btrfs filesystem resize 1:-1G /path
Shrink size of the filesystem’s device id 1 by 1GiB. The first syntax expects a device with id 1 to exist, otherwise fails. The second is equivalent and more explicit. For a single-device filesystem it’s typically not necessary to specify the devid though.
$ btrfs filesystem resize max /path
$ btrfs filesystem resize 1:max /path
Let’s assume that devid 1 exists and the filesystem does not occupy the whole block device, eg. it has been enlarged and we want to grow the filesystem. By simply using max as size we will achieve that.
There are two ways to minimize the filesystem on a given device. The btrfs inspect-internal min-dev-size command, or iteratively shrink in steps.