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 (ie. 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, eg. no journal to replay or no repairs needed. The
respective fsck utility must be run on the source filessytem 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 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

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

COPYRIGHT