Provided by: btrfs-progs_5.2.1-1ubuntu1_amd64 bug


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


       btrfs-convert [options] <device>


       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).

           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).

           The source filesystem should be clean, you are encouraged to run the fsck tool if
           you’re not sure.


       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.


       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).


       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


           disable data checksum calculations and set the NODATASUM file flag, this can speed up
           the conversion

           ignore xattrs and ACLs of files

           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

           rollback to the original ext2/3/4 filesystem if possible

       -l|--label <LABEL>
           set filesystem label during conversion

           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

           show progress of conversion (a heartbeat indicator and number of inodes processed), on
           by default

           disable progress and show only the main phases of conversion


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