BTRFS-CONVERT(8)		     BTRFS		      BTRFS-CONVERT(8)

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

SYNOPSIS
       btrfs-convert [options] <device>

DESCRIPTION
       The btrfs-convert tool can be 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

       • NTFS -- external tool https://github.com/maharmstone/ntfs2btrfs

       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 (i.e. the same that
       would be valid for mkfs.btrfs). This is typically the system page size
       (4KiB on x86_64 machines).

       NOTE:
	  Always consider if a mkfs and file copy would not be a better option
	  than the in-place conversion given what was said above. The
	  conversion depends on 3rd party libraries and the other filesystems
	  could still evolve and add new features. Not all combinations are
	  covered or tested.

       BEFORE YOU START

       The source filesystem must be clean, e.g. no journal to replay or no
       repairs needed. The respective fsck utility must be run on the source
       filesystem prior to conversion. Please refer to the manual pages in
       case you encounter problems.

       For ext2/3/4:

	  # e2fsck -fvy /dev/sdx

       For reiserfs:

	  # reiserfsck -fy /dev/sdx

       Skipping that step could lead to incorrect results on the target
       filesystem, but it may work.

       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

       --csum <type>, --checksum <type>
	      Specify the checksum algorithm. Default is crc32c. Valid values
	      are crc32c, xxhash, sha256 or blake2. To mount such filesystem
	      kernel must support the checksums as well.

       -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 16KiB (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

       --uuid <SPEC>
	      set the FSID of the new filesystem based on 'SPEC':

	      • new - (default) generate UUID for the FSID of btrfs

	      • copy - copy UUID from the source filesystem

	      • UUID - a conforming UUID value, the 36 byte string
		representation

       --version
	      Print the btrfs-convert version, builtin features and exit.

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

SEE ALSO
       mkfs.btrfs(8)

6.16.1			      September 10, 2025	      BTRFS-CONVERT(8)