NAME

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

SYNOPSIS

       btrfs-convert [options] <device>

DESCRIPTION

       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).

           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 required 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 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 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.

       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 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

EXIT STATUS

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

SEE ALSO

       mkfs.btrfs(8)