The plurality of disk devices are configured from {HEAD ~ a first disk device group} and a second disk device group having different performance to the first disk device group, typically composed of a SAS specification hard disk device group and {TAIL ~ a SATA specification hard disk device group} 
The plurality of disk devices are configured from { HEAD ~ a first disk device group } and a second disk device group having different performance to the first disk device group , typically composed of a SAS specification hard disk device group and { TAIL ~ a SATA specification hard disk device group }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL