btrfs-convert man page

btrfs-convert — convert from ext2/3/4 filesystem to btrfs


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 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.


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.


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 32M (-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. 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.

# btrfs balance start -m /mnt/btrfs


disable data checksum calculations and set 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. Se 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
show progress of conversion, on by default
disable detailed 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