Provided by: btrfs-tools_4.4-1_i386 bug

NAME

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

SYNOPSIS

       btrfs-convert [options] <device>

DESCRIPTION

       btrfs-convert is used to convert existing ext2/3/4 filesystem image to
       a btrfs filesystem in-place. The original filesystem image is
       accessible subvolume named ext2_saved as file image.

           Warning
           If you are going to perform rollback to ext2/3/4, 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 you decide not to rollback anymore, it is recommended to perform a
       few more steps to transform the btrfs filesystem to a more compact
       layout. The conversion inherits the original data block fragmentation
       and the metadata blocks are bound to the original free space layout.

       REMOVE THE ORIGINAL FILESYSTEM METADATA

       By removing the ext2_saved subvolume, all metadata of the original
       filesystem will be removed:

           # btrfs subvolume delete /mnt/ext2_saved

       At this point it’s not possible to do rollback. The filesystem is
       usable but may be impacted by the fragmentation.

       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 32M (-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. 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.

           # btrfs balance start -m /mnt/btrfs

OPTIONS

       -d|--no-datasum
           disable data checksum calculations and set 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. Se 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

       -p|--progress
           show progress of conversion, on by default

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

EXIT STATUS

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

SEE ALSO

       mkfs.btrfs(8)