-f
Allow dangerous changes, e.g. clear the seeding flag or
change fsid. Make sure that you are aware of the dangers.
-m
(since kernel: 5.0)
change fsid stored as metadata_uuid to a randomly generated
UUID, see also -U
-M <UUID>
(since kernel: 5.0)
change fsid stored as metadata_uuid to a given UUID, see also
-U
The metadata_uuid is stored only in the superblock and is a
backward incompatible change. The fsid in metadata blocks
remains unchanged and is not overwritten, thus the whole
operation is significantly faster than -U.
The new metadata_uuid can be used for mount by UUID and is
also used to identify devices of a multi-device filesystem.
-n
(since kernel: 3.14)
Enable no-holes feature (more efficient representation of
file holes), enabled by mkfs feature no-holes.
-r
(since kernel: 3.7)
Enable extended inode refs (hardlink limit per file in a
directory is 65536), enabled by mkfs feature extref.
-S <0|1>
Enable seeding on a given device. Value 1 will enable
seeding, 0 will disable it.
A seeding filesystem is forced to be mounted read-only. A new
device can be added to the filesystem and will capture all
writes keeping the seeding device intact. See also section
SEEDING DEVICE in btrfs(5).
Warning
Clearing the seeding flag on a device may be dangerous.
If a previously-seeding device is changed, all
filesystems that used that device will become
unmountable. Setting the seeding flag back will not fix
that.
A valid usecase is seeding device as a base image. Clear
the seeding flag, update the filesystem and make it
seeding again, provided that it's OK to throw away all
filesystems built on top of the previous base.
-u
Change fsid to a randomly generated UUID or continue previous
fsid change operation in case it was interrupted.
-U <UUID>
Change fsid to UUID in all metadata blocks.
The UUID should be a 36 bytes string in printf(3) format
"%08x-%04x-%04x-%04x-%012x". If there is a previous
unfinished fsid change, it will continue only if the UUID
matches the unfinished one or if you use the option -u.
All metadata blocks are rewritten, this may take some time,
but the final filesystem compatibility is unaffected, unlike
-M.
Warning
Cancelling or interrupting a UUID change operation will
make the filesystem temporarily unmountable. To fix it,
rerun btrfstune -u and let it complete.
-x
(since kernel: 3.10)
Enable skinny metadata extent refs (more efficient
representation of extents), enabled by mkfs feature
skinny-metadata.
All newly created extents will use the new representation. To
completely switch the entire filesystem, run a full balance
of the metadata. Please refer to btrfs-balance(8).
