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 filesys-
tem image to a btrfs filesystem in-place. The original filesystem im-
age 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 libreis-
erfscore 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 filesys-
tem. This will change the extent layout and make btrfs-convert un-
able to rollback.
The conversion utilizes free space of the original filesystem. The ex-
act estimate of the required space cannot be foretold. The final btrfs
metadata might occupy several gigabytes on a hundreds-gigabyte filesys-
tem.
If the ability to rollback is no longer important, the it is recom-
mended 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 filesys-
tems 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).
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 en-
tire filesystem. This will attempt to make file extents more contigu-
ous.
# 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 fragmen-
tation) 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 re-
main 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 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
EXIT STATUS
btrfs-convert will return 0 if no error happened. If any problems hap-
pened, 1 will be returned.
SEE ALSO
mkfs.btrfs(8)
6.6.3 Mar 31, 2024 BTRFS-CONVERT(8)
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