btrfs-convert - convert from ext2/3/4 or reiserfs filesystem to btrfs in-place
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
•ext2, ext3, ext4 — original
feature, always built in
•reiserfs — since version 4.13,
opptinally 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 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
). This is typically the system page size (4KiB on x86_64
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
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
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
), flush data per-file
) 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 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
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
set filesystem label during conversion
use label from the converted filesystem
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
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
will return 0 if no error happened. If any problems
happened, 1 will be returned.