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BTRFS-CONVERT(8)                 Btrfs Manual                 BTRFS-CONVERT(8)

NAME
       btrfs-convert - convert from ext2/3/4 or reiserfs filesystem to btrfs
       in-place

SYNOPSIS
       btrfs-convert [options] _device_

DESCRIPTION
       btrfs-convert 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.

       Supported filesystems:

       o   ext2, ext3, ext4 -- original feature, always built in

       o   reiserfs -- since version 4.13, optionally 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).

           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).

           Note
           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 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 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.

       -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

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

SEE ALSO
       mkfs.btrfs(8)

Btrfs v5.4.1                      01/09/2020                  BTRFS-CONVERT(8)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | SEE ALSO