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


   btrfs-convert [options] <device>


   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.

       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

   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

   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


   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.


   An optional but recommended step is to run defragmentation on the
   entire filesystem. This will attempt to make file extents more

       # 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 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 details.

       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 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

       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 returned.




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