btrfs-convert(8) - Man pages

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 libreiserf-
score 3.6.27

• NTFS -- external tool ]8;;https://github.com/maharmstone/ntfs2btrfs\https://github.com/maharmstone/ntfs2btrfs]8;;\

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 meta-
data 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 conver-
sion 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 re-
pairs 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 us-
able but may be impacted by the fragmentation inherited from the origi-
nal 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 de-
fault 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 un-
changed.

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 de-
crease 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 sec-
torsize, 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 fea-
ture, prefix it with ^. Description of the features is in sec-
tion 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 representa-
tion

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

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