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BTRFS-FILESYSTEM(8) Btrfs Manual BTRFS-FILESYSTEM(8)

NAME
btrfs-filesystem - command group that primarily does work on the whole
filesystems

SYNOPSIS
btrfs filesystem _subcommand_ _args_

DESCRIPTION
btrfs filesystem is used to perform several whole filesystem level
tasks, including all the regular filesystem operations like resizing,
space stats, label setting/getting, and defragmentation. There are
other whole filesystem tasks like scrub or balance that are grouped in
separate commands.

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:

o device size: 1.9TiB, one device, no RAID

o filesystem size: 1.9TiB

o 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

o Data, System and Metadata are separate block group types.
GlobalReserve is an artificial and internal emergency space,
see below.

o single -- the allocation profile, defined at mkfs time

o 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.

o 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 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.

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 filesystem. Requires kernel
2.6.33 and newer.

If -r is passed, files in dir will be defragmented recursively (not
descending to subvolumes and mount points). 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.

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 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.

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.
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).

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), lzo or zstd.
Currently it's not possible to select no compression. See also
section EXAMPLES.

-r
defragment files recursively in given directories, does not
descend to subvolumes or mount points

-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 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).

-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,
default: 32M

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_..]
Calculate disk usage of the target files using FIEMAP. For
individual files, it will report a count of total bytes, and
exclusive (not shared) bytes. We also calculate a set shared value
which is described below.

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.

Options

-s|--summarize
display only a total for each argument

--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.

label [_device_|_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
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 unit 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.