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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | SEE ALSO | COLOPHON |
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BTRFS-CONVERT(8) Btrfs Manual BTRFS-CONVERT(8)
btrfs-convert - convert from ext2/3/4 or reiserfs filesystem to
btrfs in-place
btrfs-convert [options] <device>
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 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 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).
# btrfs balance start -m /mnt/btrfs
--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
--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
btrfs-convert will return 0 if no error happened. If any problems
happened, 1 will be returned.
mkfs.btrfs(8)
This page is part of the btrfs-progs (btrfs filesystem tools)
project. Information about the project can be found at
⟨https://btrfs.wiki.kernel.org/index.php/Btrfs_source_repositories⟩.
If you have a bug report for this manual page, see
⟨https://btrfs.wiki.kernel.org/index.php/Problem_FAQ#How_do_I_report_bugs_and_issues.3F⟩.
This page was obtained from the project's upstream Git repository
⟨git://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git⟩
on 2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-23.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
Btrfs v5.16.1 02/06/2022 BTRFS-CONVERT(8)
Pages that refer to this page: btrfs(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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