Ubuntu Manpage: btrfs-convert - convert from ext2/3/4 or reiserfs filesystem to btrfs in-place

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 <#man-mkfs-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.

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

EXIT STATUS

SEE ALSO