btrfs-convert(8) — Linux manual page


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

NAME         top

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

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).

           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

       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).

           The source filesystem should be clean, you are encouraged to run
           the fsck tool if you’re not sure.


       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.


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

           # 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).


       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 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.

           disable data checksum calculations and set the NODATASUM file
           flag, this can speed up the conversion

           ignore xattrs and ACLs of files

           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

           rollback to the original ext2/3/4 filesystem if possible

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

           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

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

           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


COLOPHON         top

       This page is part of the btrfs-progs (btrfs filesystem tools)
       project.  Information about the project can be found at 
       If you have a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       on 2020-09-18.  (At that time, the date of the most recent commit
       that was found in the repository was 2020-07-02.)  If you discover
       any rendering problems in this HTML version of the page, or you
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       COLOPHON (which is not part of the original manual page), send a mail

Btrfs v4.6.1                     05/16/2020                 BTRFS-CONVERT(8)

Pages that refer to this page: btrfs(8)