btrfs-progs/Documentation/btrfs-convert.asciidoc

btrfs-convert(8)
================

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

SYNOPSIS
--------
*btrfs-convert* [options] <device>

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.

Due to different constraints, it's possible to convert only filesystem that
have 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 '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 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
-------
-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 turned on at conversion time. 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)