xenial (8) btrfs-filesystem.8.gz
NAME
btrfs-filesystem - command group of btrfs that usually work on the whole filesystem
SYNOPSIS
btrfs filesystem <subcommand> <args>
DESCRIPTION
btrfs filesystem is used to do the whole filesystem level tasks, including all the regular filesystem
operations like resizing, space stats, label setting/getting, and defragmentation.
SUBCOMMAND
df [options] <path>
Show a terse summary information about allocation of block group types of a given mount point. The
original purpose of this command was a debugging helper. The output needs to be further interpreted
and is not suitable for quick overview.
An example with description:
• device size: 1.9TiB, one device, no RAID
• filesystem size: 1.9TiB
• created with: mkfs.btrfs -d single -m single
$ 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
• Data, System and Metadata are separeate block group types. GlobalReserve is an artificial and
internal emergency space, see below.
• single — the allocation profile, defined at mkfs time
• total — sum of space reserved for all allocation profiles of the given type, ie. all Data/single.
Note that it’s not total size of filesystem.
• used — sum of used space of the above, ie. file extents, metadata blocks
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 global block reserve is accounted within Metadata. In case the filesystem metadata are exhausted,
GlobalReserve/total + Metadata/used = Metadata/total.
Options
-b|--raw
raw numbers in bytes, without the B suffix
-h|--human-readable
print human friendly numbers, base 1024, this is the default
-H
print human friendly numbers, base 1000
--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
-k|--kbytes
show sizes in KiB, or kB with --si
-m|--mbytes
show sizes in MiB, or MB with --si
-g|--gbytes
show sizes in GiB, or GB with --si
-t|--tbytes
show sizes in TiB, or TB with --si
If conflicting options are passed, the last one takes precedence.
defragment [options] <file>|<dir> [<file>|<dir>...]
Defragment file data on a mounted filesytem.
If -r is passed, files in dir will be defragmented recursively. The start position and the number of
bytes to defragment can be specified by start and len 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.
Warning
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 ref-links 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 ref-links.
Options
-v
be verbose, print file names as they’re submitted for defragmentation
-c[<algo>]
compress file contents while defragmenting. Optional argument selects the compression algorithm,
zlib (default) or lzo. Currently it’s not possible to select no compression. See also section
EXAMPLES.
-r
defragment files recursively in given directories
-f
flush data for each file before going to the next file. This will limit the amount of dirty data
to current file, otherwise the amount cumulates from several files and may increase system load.
-s <start>[kKmMgGtTpPeE]
defragmentation will start from the given offset, default is beginning of a file
-l <len>[kKmMgGtTpPeE]
defragment only up to len bytes, default is the file size
-t <size>[kKmMgGtTpPeE]
target extent size, do not touch extents bigger than size
For start, len, size it is possible to append units designator: 'K', 'M', 'G', 'T', 'P', or 'E',
which represent KiB, MiB, GiB, TiB, PiB, or EiB, respectively (case does not matter).
Note
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.
label [<dev>|<mountpoint>] [<newlabel>]
Show or update the label of a filesystem. This works on a mounted filesystem or a filesystem image.
The newlabel argument is optional. Current label is printed if the the argument is omitted.
Note
the maximum allowable length shall be less than 256 chars and must not contain a newline. The
trailing newline is stripped automatically.
resize [<devid>:][+/-]<size>[kKmMgGtTpPeE]|[<devid>:]max <path>
Resize a mounted filesystem identified by path. A particular device can be resized by specifying a
devid.
Warning
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.
The devid can be found in the output of btrfs filesystem show and defaults to 1 if not specified. The
size parameter specifies the new size of the filesystem. If the prefix + or - is present the size is
increased or decreased by the quantity size. If no units are specified, bytes are assumed for size.
Optionally, the size parameter may be suffixed by one of the following units designators: 'K', 'M',
'G', 'T', 'P', or 'E', which represent KiB, MiB, GiB, TiB, PiB, or EiB, respectively (case does not
matter).
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>]
Show the btrfs filesystem with some additional info about devices and space allocation.
If no option none of path/uuid/device/label is passed, information about all the BTRFS filesystems is
shown, both mounted and unmounted.
Options
-m|--mounted
probe kernel for mounted BTRFS filesystems
-d|--all-devices
scan all devices under /dev, otherwise the devices list is extracted from the /proc/partitions
file. This is a fallback option if there’s no device node manager (like udev) available in the
system.
--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
sync <path>
Force a sync of the filesystem at path. This is done via a special ioctl and will also trigger
cleaning of deleted subvolumes. Besides that it’s equivalent to the sync(1) command.
usage [options] <path> [<path>...]
Show detailed information about internal filesystem usage. This is supposed to replace the btrfs
filesystem df command in the long run.
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 fi 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)
Data ratio: 1.00
Metadata ratio: 1.00
Global reserve: 512.00MiB (used: 0.00B)
The root user will also see stats broken down by block group types:
Data,single: Size:1.15TiB, Used:1.13TiB
/dev/sdb 1.15TiB
Metadata,single: Size:12.00GiB, Used:6.45GiB
/dev/sdb 12.00GiB
System,single: Size:32.00MiB, Used:144.00KiB
/dev/sdb 32.00MiB
Unallocated:
/dev/sdb 669.99GiB
Options
-b|--raw
raw numbers in bytes, without the B suffix
-h|--human-readable
print human friendly numbers, base 1024, this is the default
-H
print human friendly numbers, base 1000
--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
-k|--kbytes
show sizes in KiB, or kB with --si
-m|--mbytes
show sizes in MiB, or MB with --si
-g|--gbytes
show sizes in GiB, or GB with --si
-t|--tbytes
show sizes in TiB, or TB with --si
-T
show data in tabular format
If conflicting options are passed, the last one takes precedence.
EXAMPLES
$ btrfs filesystem defrag -v -r dir/
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/
Recusively 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/
Recusively defragment files under dir/, be verbose, wait until all blocks are flushed and force file
compression.
$ btrfs filesystem defrag -v -r -t 64M dir/
Recusively 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, the filesystem does not occupy the whole block device, eg. it has been
enlarged and we wan the grow the filesystem. Simply using max as size we will achieve that.
Note
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.
EXIT STATUS
btrfs filesystem 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),