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