BTRFS-CONVERT(8) Btrfs Manual BTRFS-CONVERT(8)
NAME
btrfs-convert - convert from ext2/3/4 filesystem to btrfs
SYNOPSIS
btrfs-convert [options]
DESCRIPTION
btrfs-convert is used to convert existing ext2/3/4 filesystem image to a btrfs filesystem
in-place. The original filesystem image is accessible subvolume named ext2_saved as file
image.
Warning
If you are going to perform rollback to ext2/3/4, 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 you decide not to rollback anymore, it is recommended to perform a few more steps to
transform the btrfs filesystem to a more compact layout. The conversion inherits the
original data block fragmentation and the metadata blocks are bound to the original free
space layout.
REMOVE THE ORIGINAL FILESYSTEM METADATA
By removing the ext2_saved subvolume, all metadata of the original filesystem will be
removed:
# btrfs subvolume delete /mnt/ext2_saved
At this point it’s not possible to do rollback. The filesystem is usable but may be
impacted by the fragmentation.
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 32M (-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. 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.
# btrfs balance start -m /mnt/btrfs
OPTIONS
-d|--no-datasum
disable data checksum calculations and set 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. Se mkfs.btrfs(8) for more
details.
-r|--rollback
rollback to the original ext2/3/4 filesystem if possible
-l|--label