HSC70 Mass Storage Server

The HSC70 Mass Storage Server (alternatively called the HSC70 Hierarchical Storage Controller) is an intelligent mass storage sub-system server from DEC, part of the Digital Storage Architecture (DSA). It was the first commercial RAID controller; a capability termed 'shadowing' in the documentation.

The HSC70 connects with one or more host computer systems; it communicates over the Computer Interconnect (CI), via the SC008 Star Coupler (a passive, RF-transformer coupling network). The HSC was the first DEC mass storage server to connect to multiple hosts. The Mass Storage Control Protocol (MSCP) is a communication protocol used over the CI between host system(s) and the HSC70. This protocol enables a single class driver to replace multiple device-specific drivers. Separate but similar protocols exist for disk and tape communication:

• Disk MSCP frees the host from responsibility for disk I/O functions and error recovery.
• Tape MSCP includes those protocol variations necessary for tape functionality in the subsystem.

The HSC70 also connects to a set of mass storage devices. If the devices that the HSC70 controls are disk drives, the HSC70 communicates with them over the Standard Disk Interconnect (SDI) bus; if they are magnetic tape formatters, the Standard Tape Interconnect (STI) bus is used. The HSC70 can support a maximum total of eight disk and/or tape data channels (usually a minimum of two; the others are optional). Each one of the disk data channels accommodates up to four drives. Each of the tape data channels accommodates up to four formatters, each of which can handle up to four magnetic tape drives.

An HSC70 can perform up to 1,150 I/O operations per second. It contains a microprocessor; in the case of the HSSC70, this is a J-11 chip set. The HSC70 is housed in a single cabinet.

The successor model to the HSC70 was the HSC90, to which an HSC70 can be field upgraded. (An HSC50 cannot be upgraded into an HSC70.)

Further reading

• HSC User Guide (AA-GMEAA-TK)
• HSC70 Illustrated Breakdown (EK-HSC70-IP)
• HSC70 Field Print Set (MP-01426)

External links

• HSC - documentation at Bitsavers
  • HSC50/70 Hardware Technical Manual (EK-HS571-TM-OO1)
  • HSC70 Service Manual (EK-HSC70-SV-002) - replaced by the below
  • HSC Service Manual (EK-HSCMA-SV-001)
  • HSC Service Manual (EK-HSCMA-SV-002)
• HSC70 (CI Based Hierarchical Storage Controller) - Overview