To mount a multi device filesystem, there are two options. You can specify all component devices, separated by hyphens, e.g.

mount -t bcachefs /dev/sda:/dev/sdb:/dev/sdc /mnt

Or, use the mount.bcachefs tool to mount by filesystem UUID. Still todo: improve the mount.bcachefs tool to support mounting by filesystem label.

No special handling is needed for recovering from unclean shutdown. Journal replay happens automatically, and diagnostic messages in the dmesg log will indicate whether recovery was from clean or unclean shutdown.

The -o degraded option will allow a filesystem to be mounted without all the the devices, but will fail if data would be missing. The -o very_degraded can be used to attempt mounting when data would be missing.

Also relevant is the -o nochanges option. It disallows any and all writes to the underlying devices, pinning dirty data in memory as necessary if for example journal replay was necessary - think of it as a “super read-only” mode. It can be used for data recovery, and for testing version upgrades.

The -o verbose enables additional log output during the mount process.