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

NAME
       btrfs-convert - convert from ext2/3/4 filesystem to btrfs in-place
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.
       Due to different constraints, it's possible to convert only filesystem
       that have 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).
           Note
           The source filesystem should be clean, you are encouraged to run
           the fsck tool if you're not sure.
       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 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
       -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 turned on at conversion time. 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
       btrfs-convert will return 0 if no error happened. If any problems
       happened, 1 will be returned.
SEE ALSO
       mkfs.btrfs(8)

Btrfs v4.9.1                      08/06/2017                  BTRFS-CONVERT(8)