BTRFS-FILESYSTEM(8) Btrfs Manual BTRFS-FILESYSTEM(8)
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 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 taks 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 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 filesystem. Requires kernel
2.6.33 and newer.
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 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 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.
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) 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 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 fi 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. 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 [<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/
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, 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),
Btrfs v4.9.1 08/06/2017 BTRFS-FILESYSTEM(8)
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