Patent ID: 7174422

Claim:
A data storage system, comprising: a set of storage devices, each storage device being configured to store and retrieve data in response to data access commands from a set of external host computers; first-tier RAID control circuitry coupled to the set of storage devices, the first-tier RAID control circuitry being configured to apply a first RAID scheme on the set of storage devices in a manner that treats the set of storage devices as a first array under application of the first RAID scheme; and second-tier RAID control circuitry coupled to the first array of storage devices, the second-tier RAID control circuitry being configured to apply a second RAID scheme on a set of storage sub-devices of a storage device of the set of storage devices in a manner that treats the set of storage sub-devices of that storage device as a second array under application of the second RAID scheme; wherein each storage device of the set of storage devices has at least one magnetic disk drive; wherein the storage device having the set of storage sub-devices includes, as the storage sub-devices, multiple small form factor magnetic disk drives; wherein the first-tier RAID control circuitry is adapted to treat each storage device of the set of storage devices as exactly one RAID device when applying the first RAID scheme to store particular data in the set of storage devices; and wherein the second-tier RAID control circuitry is adapted to treat each storage sub-device of the set of storage sub-devices as exactly one RAID device when applying the second RAID scheme to store a portion of the particular data in the set of storage sub-devices in order to store the particular data in a RAID-within-RAID manner.