Unlike most storage arrays from other vendors, the VSP is a purpose built system designed from the ground up to be a storage array and comprised of ( where appropriate) custom logic and processor ASICs. All Hitachi midrange and enterprise storage arrays are purpose built. In the VSP (like all Hitachi designs), there are separate intelligent components from which the array is created. These components are operated in parallel to achieve high performance, scalability, and reliability. Products such as IBM’s DS8000 series, and EMC’s CX and VMAX series are essentially small servers running standard operating systems (AIX or Linux). [EMC’s DMX series was also a purpose built design.] The “storage engine” in these systems is software running in the server, controlling simple host and disk interface cards (usually FC). The server RAM holds the operating system, the storage software, the storage system metadata, and all user data in a cache. Briefly (the boards are discussed below in greater detail), the VSP is built as a single or dual chassis array, each chassis having from one to three racks. Each chassis can have one control rack and up to two disk expansion racks. The control rack has the logic box that holds all of the control boards for a chassis, along with one or two disk container boxes (DKUs). The disk expansion racks can hold three DKUs each. There are two types of DKUs: Small Form Factor (128 2.5” disks) and Large Form Factor (80 3.5” disks). When using two chassis as a single integrated array, the two units are cross connected at the Grid Switch level. The array behaves as a single unit, not as a pair of units operating as a cluster.
The VSP uses five types of logic boards:
• Grid Switches
• Data Cache Adapters (cache boards)
• Front‐end Directors (FC or FICON ports)
• Back‐end Directors (disk controllers)
• Virtual Storage Directors (processor boards).
