btrfs-convert(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | SEE ALSO | COLOPHON

BTRFS-CONVERT(8)              Btrfs Manual              BTRFS-CONVERT(8)

NAME         top

       btrfs-convert - convert from ext2/3/4 or reiserfs filesystem to
       btrfs in-place

SYNOPSIS         top

       btrfs-convert [options] <device>

DESCRIPTION         top

       btrfs-convert is used to convert existing source filesystem image
       to a btrfs filesystem in-place. The original filesystem image is
       accessible in subvolume named like ext2_saved as file image.

       Supported filesystems:

       •   ext2, ext3, ext4 — original feature, always built in

       •   reiserfs — since version 4.13, optionally built, requires
           libreiserfscore 3.6.27

       The list of supported source filesystem by a given binary is
       listed at the end of help (option --help).

           Warning
           If you are going to perform rollback to the original
           filesystem, you should not execute btrfs balance command on
           the converted filesystem. This will change the extent layout
           and make btrfs-convert unable to rollback.

       The conversion utilizes free space of the original filesystem.
       The exact estimate of the required space cannot be foretold. The
       final btrfs metadata might occupy several gigabytes on a
       hundreds-gigabyte filesystem.

       If the ability to rollback is no longer important, the it is
       recommended to perform a few more steps to transition the btrfs
       filesystem to a more compact layout. This is because the
       conversion inherits the original data blocks' fragmentation, and
       also because the metadata blocks are bound to the original free
       space layout.

       Due to different constraints, it is only possible to convert
       filesystems that have a supported data block size (ie. the same
       that would be valid for mkfs.btrfs). This is typically the system
       page size (4KiB on x86_64 machines).

       BEFORE YOU START

       The source filesystem must be clean, eg. no journal to replay or
       no repairs needed. The respective fsck utility must be run on the
       source filesytem prior to conversion. Please refer to the manual
       pages in case you encounter problems.

       For ext2/3/4:

           # e2fsck -fvy /dev/sdx

       For reiserfs:

           # reiserfsck -fy /dev/sdx

       Skipping that step could lead to incorrect results on the target
       filesystem, but it may work.

       REMOVE THE ORIGINAL FILESYSTEM METADATA

       By removing the subvolume named like ext2_saved or
       reiserfs_saved, all metadata of the original filesystem will be
       removed:

           # btrfs subvolume delete /mnt/ext2_saved

       At this point it is not possible to do a rollback. The filesystem
       is usable but may be impacted by the fragmentation inherited from
       the original filesystem.

       MAKE FILE DATA MORE CONTIGUOUS

       An optional but recommended step is to run defragmentation on the
       entire filesystem. This will attempt to make file extents more
       contiguous.

           # btrfs filesystem defrag -v -r -f -t 32M /mnt/btrfs

       Verbose recursive defragmentation (-v, -r), flush data per-file
       (-f) with target extent size 32MiB (-t).

       ATTEMPT TO MAKE BTRFS METADATA MORE COMPACT

       Optional but recommended step.

       The metadata block groups after conversion may be smaller than
       the default size (256MiB or 1GiB). Running a balance will attempt
       to merge the block groups. This depends on the free space layout
       (and fragmentation) and may fail due to lack of enough work
       space. This is a soft error leaving the filesystem usable but the
       block group layout may remain unchanged.

       Note that balance operation takes a lot of time, please see also
       btrfs-balance(8).

           # btrfs balance start -m /mnt/btrfs

OPTIONS         top

       --csum <type>, --checksum <type>
           Specify the checksum algorithm. Default is crc32c. Valid
           values are crc32c, xxhash, sha256 or blake2. To mount such
           filesystem kernel must support the checksums as well.

       -d|--no-datasum
           disable data checksum calculations and set the NODATASUM file
           flag, this can speed up the conversion

       -i|--no-xattr
           ignore xattrs and ACLs of files

       -n|--no-inline
           disable inlining of small files to metadata blocks, this will
           decrease the metadata consumption and may help to convert a
           filesystem with low free space

       -N|--nodesize <SIZE>
           set filesystem nodesize, the tree block size in which btrfs
           stores its metadata. The default value is 16KB (16384) or the
           page size, whichever is bigger. Must be a multiple of the
           sectorsize, but not larger than 65536. See mkfs.btrfs(8) for
           more details.

       -r|--rollback
           rollback to the original ext2/3/4 filesystem if possible

       -l|--label <LABEL>
           set filesystem label during conversion

       -L|--copy-label
           use label from the converted filesystem

       -O|--features <feature1>[,<feature2>...]
           A list of filesystem features enabled the at time of
           conversion. Not all features are supported by old kernels. To
           disable a feature, prefix it with ^. Description of the
           features is in section FILESYSTEM FEATURES of mkfs.btrfs(8).

           To see all available features that btrfs-convert supports
           run:

           btrfs-convert -O list-all

       -p|--progress
           show progress of conversion (a heartbeat indicator and number
           of inodes processed), on by default

       --no-progress
           disable progress and show only the main phases of conversion

EXIT STATUS         top

       btrfs-convert will return 0 if no error happened. If any problems
       happened, 1 will be returned.

SEE ALSO         top

       mkfs.btrfs(8)

COLOPHON         top

       This page is part of the btrfs-progs (btrfs filesystem tools)
       project.  Information about the project can be found at 
       ⟨https://btrfs.wiki.kernel.org/index.php/Btrfs_source_repositories⟩.
       If you have a bug report for this manual page, see
       ⟨https://btrfs.wiki.kernel.org/index.php/Problem_FAQ#How_do_I_report_bugs_and_issues.3F⟩.
       This page was obtained from the project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git⟩
       on 2021-04-01.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-03-24.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

Btrfs v4.6.1                   04/01/2021               BTRFS-CONVERT(8)

Pages that refer to this page: btrfs(8)