btrfs-filesystem - Man Page

command group that primarily does work on the whole filesystems

Examples (TL;DR)

tldr.sh

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:

  • 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 separate 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, i.e. all Data/single. Note that it's not total size of filesystem.
  • used -- sum of used space of the above, i.e. file extents, metadata blocks

GlobalReserve is an artificial and internal emergency space. It is used e.g. 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, 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 256KiB 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

-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 (i.e. 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: 32MiB

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.

--step SIZE

Perform defragmention in the range in SIZE steps and flush (-f) after each one. The range is default (the whole file) or given by -s and -l, split into the steps or done in one go if the step is larger. Minimum range size is 256KiB.

-v

(deprecated) alias for global -v option

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.

mkswapfile [-s size] file

Create a new file that's suitable and formatted as a swapfile. Default size is 2GiB, fixed page size 4KiB, minimum size is 40KiB.

A swapfile must be created in a specific way: NOCOW and preallocated. Subvolume containing a swapfile cannot be snapshotted and blocks of an activated swapfile cannot be balanced.

Swapfile creation can be achieved by standalone commands too. Activation needs to be done by command swapon(8). See also command btrfs inspect-internal map-swapfile and the Swapfile feature description.

NOTE:

The command is a simplified version of 'mkswap', if you want to set label, page size, or other parameters please use 'mkswap' proper.

Options

-s|--size SIZE

Create swapfile of a given size SIZE (accepting k/m/g/e/p suffix).

-U|--uuid UUID

specify UUID to use, or a special value: clear (all zeros), random, time (time-based random)

resize [options] [<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 expand the partition before enlarging the filesystem and shrink the partition after reducing the size of the filesystem.  This can be 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.

The size of the portion that the filesystem uses of an underlying device can be determined via the btrfs filesystem show --raw command on the filesystem’s mount point (where it’s given for each devid after the string size or via the btrfs inspect-internal dump-super command on the specific device (where it’s given as the value of dev_item.total_bytes, which is not to be confused with total_bytes). The value is also the address of the first byte not used by the filesystem.

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.

Note that there's a lower limit on the new size (either specified as an absolute size or difference) that is checked by kernel and rejected eventually as invalid. Lower values will print a warning but still pass the request to kernel. The currently known value is 256MiB.

See also section Examples.

Options

--enqueue

wait if there's another exclusive operation running, otherwise continue

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, similar to the sync(1) command. In addition, it starts cleaning of deleted subvolumes. To wait for the subvolume deletion to complete use the btrfs subvolume sync 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 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
    Device slack:                  1.00GiB
    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
  • Device size -- sum of raw device capacity available to the filesystem, note that this may not be the same as the total device size (the difference is accounted as slack)
  • Device allocated -- sum of total space allocated for data/metadata/system profiles, this also accounts space reserved but not yet used for extents
  • Device unallocated -- the remaining unallocated space for future allocations (difference of the above two numbers)
  • Device missing -- sum of capacity of all missing devices
  • Device slack -- sum of slack space on all devices (difference between entire device size and the space occupied by filesystem)
  • Used -- sum of the used space of data/metadata/system profiles, not including the reserved space
  • Free (estimated) -- approximate size of the remaining free space usable for data, including currently allocated space and estimating the usage of the unallocated space based on the block group profiles, the min is the lower bound of the estimate in case multiple profiles are present
  • Free (statfs, df) -- the amount of space available for data as reported by the statfs/statvfs syscall, also returned as Avail in the output of df. The value is calculated in a different way and may not match the estimate in some cases (e.g.  multiple profiles).
  • Data ratio -- ratio of total space for data including redundancy or parity to the effectively usable data space, e.g. single is 1.0, RAID1 is 2.0 and for RAID5/6 it depends on the number of devices
  • Metadata ratio -- ditto, for metadata
  • Global reserve -- portion of metadata currently used for global block reserve, used for emergency purposes (like deletion on a full filesystem)
  • Multiple profiles -- what block group types (data, metadata) have more than one profile (single, raid1, ...), see btrfs(5) section FILESYSTEMS WITH MULTIPLE PROFILES.

And on a zoned filesystem there are two more lines in the Device section:

Device zone unusable:          5.13GiB
Device zone size:            256.00MiB
  • Device zone unusable -- sum of of space that's been used in the past but now is not due to COW and not referenced anymore, the chunks have to be reclaimed and zones reset to make it usable again
  • Device zone size -- the reported zone size of the host-managed device, same for all devices

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.

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 and the filesystem does not occupy the whole block device, e.g. it has been enlarged and we want to grow the filesystem. By 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 documentation at https://btrfs.readthedocs.io.

See Also

btrfs-subvolume(8), mkfs.btrfs(8)

Referenced By

btrfs(8), btrfs-replace(8).

Sep 17, 2024 6.11 BTRFS