Digital Storage Systems Interconnect
Encyclopedia
The Digital Storage Systems Interconnect (DSSI) is a bus developed by Digital Equipment Corporation
for connecting storage devices and clustering VAX
systems and support was extended to MIPS based DECsystem
and later to Alpha processor based AlphaServer
systems.
It was introduced in 1988 and has a bandwidth of 32 Mbit/s and was typically limited to a length of 25 meters.
DSSI peripherals could be distinguished from narrow SCSI devices by their characteristic five conductor power connector featuring an extra lead intended for Battery/UPS connection to power critical components in the event of a power failure.
o Eight-bit data path
o Up to eight nodes on the bus including variable numbers of initiators and targets
o Distributed arbitration
o Peak bandwidth of 4 megabytes per second
o All systems connected to the same DSSI bus must have a common power/ground.
o "The Q-Bus
5-Enclosure Rule": For Q-bus VMScluster configurations, a maximum of five
enclosures, _excluding_ SF200/210s, can be configured on a single DSSI bus. Note that
only _one_ (1) SF100 is allowed on any DSSI bus.
o "The VAX 6000
Cabinet Rule": For a VAX 6000 DSSI VMScluster system, a maximum of two
or three VAX 6000 systems and one storage cabinet, typically an SF200 or SF210, can be
configured on a single DSSI bus.
o Maximum DSSI bus length cannot exceed 27 meters (89 feet) and ground offset voltage cannot
exceed 30mv (dc) or 10.5mv (rms).
Bus Length Allowable Offset
Meters/Feet (DC) (AC)
----------- ----------------
up to 20/65 200mv 70mv (rms)
20-25/65-82 40mv 14mv (rms)
VAX6000 QUAD-Host--> 27/89 30mv 10.5mv (rms)
VAX7000
VAX10000
:
OpenVMS VAX V5.0-2:
o Single- and Dual-Host support with 2 EDA640s (MicroVAX
3300/3400
series).
o Systems Communications Services (SCS) for the VMScluster is run
over the Network Interconnect (NI) for MicroVAX 3300/3400.
OpenVMS VAX V5.1:
o Standalone support for the KFQSA.
o Up to 6 ISEs on a single DSSI bus regardless of whether 1 or 2
hosts systems are attached to the bus.
OpenVMS VAX V5.1-1:
o Dual host support for KFQSAs (1 KFQSA per system).
OpenVMS VAX V5.2:
o For 3300/3400 series, SCS communication over the DSSI.
o Multiple KFQSA's per system, but *not* multiple dual-hosted
DSSI's per system (here, multiple means 2, since only 2 hosts
are allowed on the DSSI bus).
o DSSI adapter must connect to another like adapter, e.g. EDA640
to EDA640 or KFQSA to KFQSA.
o Up to 7 ISEs on a single DSSI bus when only 1 host system is
attached to the bus.
OpenVMS VAX V5.3:
o Mixed DSSI adapters, i.e. EDA640 to KFQSA.
o Mixed DSSI adapters, i.e. EDA640 to KFQSA.
o Double dual-host configurations, i.e. 2 DSSI buses between two
CPUs. Each bus is terminated at its own pair of adapters.
OpenVMS VAX V5.3-2:
o Support for VAX 4000. (The VAX 4000 has 2 SHACs and can support
two KFQSAs on the bus, so it can have up to 4 DSSI buses).
OpenVMS VAX V5.4-2:
o Support for the KFMSA, an XMI to DSSI adapter. The KFMSA may
only be used to single-host a VAX 6000 model or dual-host 2 VAX
6000 models together.
OpenVMS VAX V5.4-3:
o Tri-host configurations supported.
OpenVMS VAX V5.5-2:
o Quad-host configurations with VAX 6000, VAX 7000/10000
series systems now supported.
NOTE: KFQSAs do not support SCS communication over the DSSI bus,
they MUST have a NI connection in order to run the cluster
software.
OpenVMS Alpha V1.5, OpenVMS VAX V6.0:
o Quad-host DSSI configurations with DEC 4000 AXP
systems supported.
DEC 4000 systems can be configured only as end nodes on a DSSI
bus, therefore, quad-host configurations must include at least
two VAX systems.
o KFQSA Q-bus to DSSI configurations supported.
VAX processors that use the KFQSA adapter can be placed on the
same DSSI bus as DEC 4000 processors.
and Symbios Logic
made DSSI compatible chipsets or peripherals, for example,
CMD manufactured various models of the CDI-4000 which would allow SCSI
peripherals to be used on a DSSI bus.
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
for connecting storage devices and clustering VAX
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...
systems and support was extended to MIPS based DECsystem
DECsystem
DECsystem was a line of server computers from Digital Equipment Corporation. They were based on MIPS architecture processors and ran DEC's version of the UNIX operating system, called Ultrix...
and later to Alpha processor based AlphaServer
AlphaServer
AlphaServer was the name given to a series of server computers, produced from 1994 onwards by Digital Equipment Corporation, and latterly by Compaq and HP. As the name suggests, the AlphaServers were based on the DEC Alpha 64-bit microprocessor...
systems.
It was introduced in 1988 and has a bandwidth of 32 Mbit/s and was typically limited to a length of 25 meters.
DSSI peripherals could be distinguished from narrow SCSI devices by their characteristic five conductor power connector featuring an extra lead intended for Battery/UPS connection to power critical components in the event of a power failure.
Characteristics
The major characteristics of the DSSI bus are:o Eight-bit data path
o Up to eight nodes on the bus including variable numbers of initiators and targets
o Distributed arbitration
o Peak bandwidth of 4 megabytes per second
o All systems connected to the same DSSI bus must have a common power/ground.
o "The Q-Bus
Q-Bus
The Q-bus was one of several bus technologies used with PDP and MicroVAX computer systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts....
5-Enclosure Rule": For Q-bus VMScluster configurations, a maximum of five
enclosures, _excluding_ SF200/210s, can be configured on a single DSSI bus. Note that
only _one_ (1) SF100 is allowed on any DSSI bus.
o "The VAX 6000
VAX 6000
The VAX 6000 was a family of minicomputers developed and manufactured by Digital Equipment Corporation using processors implementing the VAX instruction set architecture...
Cabinet Rule": For a VAX 6000 DSSI VMScluster system, a maximum of two
or three VAX 6000 systems and one storage cabinet, typically an SF200 or SF210, can be
configured on a single DSSI bus.
o Maximum DSSI bus length cannot exceed 27 meters (89 feet) and ground offset voltage cannot
exceed 30mv (dc) or 10.5mv (rms).
Bus Length Allowable Offset
Meters/Feet (DC) (AC)
----------- ----------------
up to 20/65 200mv 70mv (rms)
20-25/65-82 40mv 14mv (rms)
VAX6000 QUAD-Host--> 27/89 30mv 10.5mv (rms)
VAX7000
VAX10000
Operating system support in VAX/OpenVMS
DSSI SUPPORT IN OpenVMSOpenVMS
OpenVMS , previously known as VAX-11/VMS, VAX/VMS or VMS, is a computer server operating system that runs on VAX, Alpha and Itanium-based families of computers. Contrary to what its name suggests, OpenVMS is not open source software; however, the source listings are available for purchase...
:
OpenVMS VAX V5.0-2:
o Single- and Dual-Host support with 2 EDA640s (MicroVAX
MicroVAX
The MicroVAX was a family of low-end minicomputers developed and manufactured by Digital Equipment Corporation . The first model, the MicroVAX I, was introduced in 1984...
3300/3400
series).
o Systems Communications Services (SCS) for the VMScluster is run
over the Network Interconnect (NI) for MicroVAX 3300/3400.
OpenVMS VAX V5.1:
o Standalone support for the KFQSA.
o Up to 6 ISEs on a single DSSI bus regardless of whether 1 or 2
hosts systems are attached to the bus.
OpenVMS VAX V5.1-1:
o Dual host support for KFQSAs (1 KFQSA per system).
OpenVMS VAX V5.2:
o For 3300/3400 series, SCS communication over the DSSI.
o Multiple KFQSA's per system, but *not* multiple dual-hosted
DSSI's per system (here, multiple means 2, since only 2 hosts
are allowed on the DSSI bus).
o DSSI adapter must connect to another like adapter, e.g. EDA640
to EDA640 or KFQSA to KFQSA.
o Up to 7 ISEs on a single DSSI bus when only 1 host system is
attached to the bus.
OpenVMS VAX V5.3:
o Mixed DSSI adapters, i.e. EDA640 to KFQSA.
o Mixed DSSI adapters, i.e. EDA640 to KFQSA.
o Double dual-host configurations, i.e. 2 DSSI buses between two
CPUs. Each bus is terminated at its own pair of adapters.
OpenVMS VAX V5.3-2:
o Support for VAX 4000. (The VAX 4000 has 2 SHACs and can support
two KFQSAs on the bus, so it can have up to 4 DSSI buses).
OpenVMS VAX V5.4-2:
o Support for the KFMSA, an XMI to DSSI adapter. The KFMSA may
only be used to single-host a VAX 6000 model or dual-host 2 VAX
6000 models together.
OpenVMS VAX V5.4-3:
o Tri-host configurations supported.
OpenVMS VAX V5.5-2:
o Quad-host configurations with VAX 6000, VAX 7000/10000
VAX 7000/10000
The VAX 7000 and VAX 10000 were a series of high-end multiprocessor minicomputers developed and manufactured by Digital Equipment Corporation , introduced in July 1992. These systems used microprocessors implementing the VAX instruction set architecture...
series systems now supported.
NOTE: KFQSAs do not support SCS communication over the DSSI bus,
they MUST have a NI connection in order to run the cluster
software.
OpenVMS Alpha V1.5, OpenVMS VAX V6.0:
o Quad-host DSSI configurations with DEC 4000 AXP
DEC 4000 AXP
The DEC 4000 AXP is a series of departmental server computers developed and manufactured by Digital Equipment Corporation introduced on 10 November 1992...
systems supported.
DEC 4000 systems can be configured only as end nodes on a DSSI
bus, therefore, quad-host configurations must include at least
two VAX systems.
o KFQSA Q-bus to DSSI configurations supported.
VAX processors that use the KFQSA adapter can be placed on the
same DSSI bus as DEC 4000 processors.
Third Party Peripherals
Other companies, such as CMDSilicon Image Inc.
Silicon Image is a provider of wireless and wired connectivity solutions that enable the reliable distribution and presentation of high-definition content for consumer electronics, mobile, and PC markets...
and Symbios Logic
Symbios Logic
Symbios Logic was a manufacturer of SCSI host adapter chipsets and disk array storage subsystems. It was originally established as a division of NCR Corporation in 1972, before NCR's takeover by AT&T in 1991....
made DSSI compatible chipsets or peripherals, for example,
CMD manufactured various models of the CDI-4000 which would allow SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
peripherals to be used on a DSSI bus.
See also
- DSSI VAXcluster Installation and Troubleshooting manual, EK-410AB-MG
- DEC Technical article: [ UltrixUltrixUltrix was the brand name of Digital Equipment Corporation's native Unix systems. While ultrix is the Latin word for avenger, the name was chosen solely for its sound.-History:...
] How To Configure a kfqsa on a DECstation (sic) 5500 (DS5500), Last Technical Review: 6-SEP-1991 Size: 110 lines - DEC Technical article: [OpenVMS] Configuring RF Drives Connected To DSSI Adapter In A Cluster, Last Technical Review: 8-OCT-1996 Size: 332 lines
- DEC Technical article: [OpenVMS] Guide To DSSI VAXcluster Configurations
- DEC Technical article: How To Initialize An RF72 For High Speed Mode
- DEC Technical article: [OpenVMS] Chart Overview Of Digital Disk Drive Storage Capacities
- DEC Technical article: [PERFORMANCE] Disk Drive Performance Specifications
- "OpenVMS Release Notes Addendum for VMSclusterVMSclusterA VMScluster is a computer cluster involving a group of computers running the OpenVMS operating system. Whereas tightly coupled multiprocessor systems run a single copy of the operating system, a VMScluster is loosely coupled: each machine runs its own copy of OpenVMS, but the disk storage, lock...
Systems", October 1993, (AA-Q1X7A-TE). - "Dual-Host MicroVAX Systems", VAXcluster Systems Quorum, February 1990, (EC-P0623-57), pp. 3-31.
- "VAX 4000VAX 4000The VAX 4000 was a family of low-end minicomputers developed and manufactured by Digital Equipment Corporation using microprocessors implementing the VAX instruction set architecture . The VAX 4000 succeeded the MicroVAX family...
Systems Info Sheet", (EC-F1424-41). - "VAX 6000 Systems Info Sheet", (EC-F1417-46).
- "KFESA DSSI Adapter Installation and User's Guide", May 1994, EK-KFESA-OP.A01.
- CDI-4000 DSSI to SCSI Adapter User's Manual, MAN-004000-000