There are two scenarios for marking an active disk faulty:
When the MD region has at least one spare disk, the active disk will be swapped with a spare disk.
When the MD region has no spare disks, the active disk will be marked faulty and the MD array will operate in degraded mode.
When the active disk is successfully marked faulty, it can be immediately removed from the MD region. Alternatively, the faulty disk can be later removed, as described in Section B.4.