If it doesn't do that then When creating a RAID5 array, mdadm will automatically create a degraded array with an extra spare. Raid5 is designed to provide redundancy to survive the failure of one device.System 7 – System 7.5.1 was the first to refer to itself as Mac OS, Mac OS 7.6 was the first to be branded as 'Mac OS' Mac OS 8 Mac OS 9 – Mac OS 9.2.2 was the last version of Classic Mac OS Mac OS X / OS X / macOS.