【Hitachi】 A-6511，A-6521 Disk Array Units

The A-6511 was a compact disk array subsystem announced by Hitachi in November 1992.
Because of the development of high-speed, large-scale networks and improvements in CPU performance, external memory storage units with large capacities, fast transfer speeds, and high reliability were in demand for workstation file servers, image processing systems, and other types of systems. The A-6511 was developed to meet these demands for more storage, higher performance, and greater reliability.
The A-6511 was given large storage capacity and fast data transfer speeds through parallel processing using multiple compact magnetic disk units. Furthermore, duplicate copies of data were automatically generated on redundant disks, which enabled the A-6511 to recover from a single disk failure without losing user data.

The A-6511 had the following features:

• （1）Host connections were simplified with the provision of a standard SCSI-2 interface for small systems.
• （2）Despite its compact size, the A-6511 stored up to 34 GB of file data.
• （3）The unit was suitable for image processing and other high-speed processes because it used groups of six magnetic disks in parallel to achieve continuous read and write speeds as fast as 10 MB per second.
• （4）There was one redundant disk for each disk group so that data could continue to be read and written without interrupting system processing should one disk fail.
• （5）Data from a failed disk was restored on the spare disk found in each disk group, enabling the unit to quickly return to normal operation and prevent the loss of user data.

The A-6521 was a high-performance disk subsystem announced by Hitachi in November 1992.
The A-6521 achieved a dramatic leap in data processing ability with the use of a 64 MB nonvolatile cache in its full configuration to eliminate performance bottlenecks at the internal magnetic disks. The disk subsystem was developed to boost the online transaction processing functions of network systems that were growing increasingly sophisticated.

The A-6521 had the following features:

（1）In its full configuration, it used four of the latest high-speed, large-capacity 5.25-inch dual-port magnetic disks.

（2）The maximum storage capacity was 11.4 GB.

（3）The A-6521 used a high-performance, RISC-based microprocessor that gave richer command processing functions, faster caching operations, and faster responses.

（4）It maintained easy connectivity with conventional systems with the inclusion of an industry-standard interface (SCSI-2).

Specifications of the A-6521 disk array unit

Model name	A-6521-5	A-6521-11
Host interface	SCSI-2
Subsystem capacity	5.7GB	11.4GB
Cache size	16 — 64MB
External dimensions [mm]	250 x 600 x 600 (w x d x h)