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https://github.com/kdave/btrfs-progs
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134 lines
4.7 KiB
Plaintext
134 lines
4.7 KiB
Plaintext
btrfs-convert(8)
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================
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NAME
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----
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btrfs-convert - convert from ext2/3/4 or reiserfs filesystem to btrfs in-place
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SYNOPSIS
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--------
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*btrfs-convert* [options] <device>
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DESCRIPTION
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-----------
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*btrfs-convert* is used to convert existing source filesystem image to a btrfs
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filesystem in-place. The original filesystem image is accessible in subvolume
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named like 'ext2_saved' as file 'image'.
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Supported filesystems:
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* ext2, ext3, ext4 -- original feature, always built in
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* reiserfs -- since version 4.13, optionally built, requires libreiserfscore 3.6.27
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The list of supported source filesystem by a given binary is listed at the end
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of help (option '--help').
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WARNING: If you are going to perform rollback to the original filesystem, you
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should not execute *btrfs balance* command on the converted filesystem. This
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will change the extent layout and make *btrfs-convert* unable to rollback.
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The conversion utilizes free space of the original filesystem. The exact
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estimate of the required space cannot be foretold. The final btrfs metadata
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might occupy several gigabytes on a hundreds-gigabyte filesystem.
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If the ability to rollback is no longer important, the it is recommended to
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perform a few more steps to transition the btrfs filesystem to a more compact
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layout. This is because the conversion inherits the original data blocks'
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fragmentation, and also because the metadata blocks are bound to the original
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free space layout.
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Due to different constraints, it is only possible to convert filesystems that
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have a supported data block size (ie. the same that would be valid for
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'mkfs.btrfs'). This is typically the system page size (4KiB on x86_64
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machines).
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NOTE: The source filesystem should be clean, you are encouraged to run the
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'fsck' tool if you're not sure.
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**REMOVE THE ORIGINAL FILESYSTEM METADATA**
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By removing the subvolume named like 'ext2_saved' or 'reiserfs_saved', all
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metadata of the original filesystem will be removed:
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# btrfs subvolume delete /mnt/ext2_saved
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At this point it is not possible to do a rollback. The filesystem is usable but
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may be impacted by the fragmentation inherited from the original filesystem.
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**MAKE FILE DATA MORE CONTIGUOUS**
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An optional but recommended step is to run defragmentation on the entire
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filesystem. This will attempt to make file extents more contiguous.
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# btrfs filesystem defrag -v -r -f -t 32M /mnt/btrfs
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Verbose recursive defragmentation ('-v', '-r'), flush data per-file ('-f') with
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target extent size 32MiB ('-t').
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**ATTEMPT TO MAKE BTRFS METADATA MORE COMPACT**
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Optional but recommended step.
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The metadata block groups after conversion may be smaller than the default size
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(256MiB or 1GiB). Running a balance will attempt to merge the block groups.
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This depends on the free space layout (and fragmentation) and may fail due to
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lack of enough work space. This is a soft error leaving the filesystem usable
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but the block group layout may remain unchanged.
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Note that balance operation takes a lot of time, please see also
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`btrfs-balance`(8).
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# btrfs balance start -m /mnt/btrfs
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OPTIONS
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-------
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--csum <type>::
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--checksum <type>::
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Specify the checksum algorithm. Default is 'crc32c'. Valid values are 'crc32c',
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'xxhash', 'sha256' or 'blake2'. To mount such filesystem kernel must support the
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checksums as well.
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-d|--no-datasum::
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disable data checksum calculations and set the NODATASUM file flag, this can speed
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up the conversion
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-i|--no-xattr::
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ignore xattrs and ACLs of files
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-n|--no-inline::
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disable inlining of small files to metadata blocks, this will decrease the metadata
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consumption and may help to convert a filesystem with low free space
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-N|--nodesize <SIZE>::
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set filesystem nodesize, the tree block size in which btrfs stores its metadata.
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The default value is 16KB (16384) or the page size, whichever is bigger.
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Must be a multiple of the sectorsize, but not larger than 65536. See
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`mkfs.btrfs`(8) for more details.
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-r|--rollback::
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rollback to the original ext2/3/4 filesystem if possible
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-l|--label <LABEL>::
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set filesystem label during conversion
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-L|--copy-label::
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use label from the converted filesystem
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-O|--features <feature1>[,<feature2>...]::
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A list of filesystem features enabled the at time of conversion. Not all features
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are supported by old kernels. To disable a feature, prefix it with '^'.
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Description of the features is in section 'FILESYSTEM FEATURES' of
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`mkfs.btrfs`(8).
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+
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To see all available features that btrfs-convert supports run:
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+
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+btrfs-convert -O list-all+
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+
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-p|--progress::
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show progress of conversion (a heartbeat indicator and number of inodes
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processed), on by default
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--no-progress::
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disable progress and show only the main phases of conversion
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EXIT STATUS
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-----------
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*btrfs-convert* will return 0 if no error happened.
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If any problems happened, 1 will be returned.
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SEE ALSO
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--------
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`mkfs.btrfs`(8)
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