# btrfs-convert(8) - man - phpMan [BTRFS-CONVERT(8)](https://www.chedong.com/phpMan.php/man/BTRFS-CONVERT/8/markdown) Btrfs Manual [BTRFS-CONVERT(8)](https://www.chedong.com/phpMan.php/man/BTRFS-CONVERT/8/markdown) ## NAME btrfs-convert - convert from ext2/3/4 or reiserfs filesystem to btrfs in-place ## SYNOPSIS **btrfs-convert** [options] __ ## 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: • ext2, ext3, ext4 — original feature, always built in • reiserfs — since version 4.13, optionally built, requires libreiserfscore 3.6.27 • ntfs — external tool **** 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 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)](https://www.chedong.com/phpMan.php/man/btrfs-balance/8/markdown). # btrfs balance start -m /mnt/btrfs ## OPTIONS --csum __, --checksum __ 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 __ 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)](https://www.chedong.com/phpMan.php/man/mkfs.btrfs/8/markdown) for more details. -r|--rollback rollback to the original ext2/3/4 filesystem if possible -l|--label _