Provided by: btrfs-tools_4.4-1_amd64 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)