Yesterday I received a call about a drive failure in a CLARiiON CX3-80 storage array. Since every system has at least a couple of hot spares configured, usually this does not pose a problem. But this drive failure happened on drive position 0_0_0: a vault drive failure.
The vault drives host (amongst others) the operating system and configuration of the storage array. They are also used to destage the write cache in case of an event that might threaten data integrity.