man > btrfs-convert(8)

BTRFS-CONVERT(8)                                BTRFS                               BTRFS-CONVERT(8)

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

SYNOPSIS
       btrfs-convert [options] <device>

DESCRIPTION
       The  btrfs-convert  tool  can  be 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

       • NTFS -- external tool https://github.com/maharmstone/ntfs2btrfs

       The  list  of supported source filesystem by a given binary is listed at the end of help (op‐
       tion --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  re‐
       quired 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  sup‐
       ported  data block size (i.e. 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, e.g. no journal to replay or no repairs needed. The  re‐
       spective  fsck utility must be run on the source filesystem 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 origi‐
       nal 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  im‐
       pacted 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
       --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 16KiB (16384) or the page size, whichever is bigger.  Must be a  mul‐
              tiple  of  the  sectorsize,  but not larger than 65536. See mkfs.btrfs(8) for more de‐
              tails.

       -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

       --uuid <SPEC>
              set the FSID of the new filesystem based on 'SPEC':

              • new - (default) generate UUID for the FSID of btrfs

              • copy - copy UUID from the source filesystem

              • UUID - a conforming UUID value, the 36 byte string representation

EXIT STATUS
       btrfs-convert will return 0 if no error happened.  If any problems happened, 1  will  be  re‐
       turned.

SEE ALSO
       mkfs.btrfs(8)


6.6.3                                       Mar 31, 2024                            BTRFS-CONVERT(8)