-S

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 writeskeeping the seeding device intact.

-r

(since kernel: 3.7)Enable extended inode refs (hardlink limit per file in a directory is 65536), enabled by mkfs feature extref.

-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 themetadata. Please refer to btrfs-balance(8).

-n

(since kernel: 3.14)Enable no-holes feature (more efficient representation of file holes), enabled by mkfs feature no-holes.

-f

Allow dangerous changes, e.g. clear the seeding flag or change fsid. Make sure that you are aware of the dangers.

-u

Change fsid to a randomly generated UUID or continue previous fsid change operation in case it was interrupted.

-U

Change fsid to UUID.The UUID should be a 36 bytes string in printf(3) format "%08x-%04x-%04x-%04x-%012x". If there is a previous unfinished fsidchange, it will continue only if the UUID matches the unfinished one or if you use the option -u.WarningCancelling or interrupting a UUID change operation will make the filesystem temporarily unmountable. To fix it, rerun btrfstune