The Digital Storage Systems Interconnect (DSSI) is a computer bus developed by Digital Equipment Corporation for connecting storage devices and clustering VAX systems. It was designed as a smaller and lower-cost replacement for the earlier DEC Computer Interconnect that would be more suitable for use in office environments. DSSI was superseded by Parallel SCSI.[1]
It was introduced in 1988 and has a bandwidth of 32 Mbit/s (4 MB/sec) and was typically limited to a length of 25 metres (82 ft). DSSI support was later extended to MIPS-based DECsystems and DEC Alpha-based AlphaServer systems.
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.
Up to eight nodes on the bus including variable numbers of initiators and targets
Distributed arbitration
Peak bandwidth of 4 megabytes per second
All systems connected to the same DSSI bus must have a common power/ground.
"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.
"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.
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/OpenVMSedit
DSSI SUPPORT IN OpenVMS: 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.
Third Party Peripheralsedit
Other companies, such as CMD 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.
See alsoedit
DSSI VAXcluster Installation and Troubleshooting manual, EK-410AB-MG
DEC Technical article: [ Ultrix ] 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 VMScluster Systems", October 1993, (AA-Q1X7A-TE).
"Dual-Host MicroVAX Systems", VAXcluster Systems Quorum, February 1990, (EC-P0623-57), pp. 3–31.
"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
Referencesedit
^"Digital Storage Systems Interconnect". Gordon Bell.
January 01, 1970
digital, storage, systems, interconnect, dssi, computer, developed, digital, equipment, corporation, connecting, storage, devices, clustering, systems, designed, smaller, lower, cost, replacement, earlier, computer, interconnect, that, would, more, suitable, o. The Digital Storage Systems Interconnect DSSI is a computer bus developed by Digital Equipment Corporation for connecting storage devices and clustering VAX systems It was designed as a smaller and lower cost replacement for the earlier DEC Computer Interconnect that would be more suitable for use in office environments DSSI was superseded by Parallel SCSI 1 It was introduced in 1988 and has a bandwidth of 32 Mbit s 4 MB sec and was typically limited to a length of 25 metres 82 ft DSSI support was later extended to MIPS based DECsystems and DEC Alpha based AlphaServer systems 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 Contents 1 Characteristics 2 Operating system support in VAX OpenVMS 3 Third Party Peripherals 4 See also 5 ReferencesCharacteristics editThe major characteristics of the DSSI bus are Eight bit data path Up to eight nodes on the bus including variable numbers of initiators and targets Distributed arbitration Peak bandwidth of 4 megabytes per second All systems connected to the same DSSI bus must have a common power ground 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 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 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 gt 27 89 30mv 10 5mv rms VAX7000 VAX10000Operating system support in VAX OpenVMS editDSSI SUPPORT IN OpenVMS 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 Third Party Peripherals editOther companies such as CMD 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 See also editDSSI VAXcluster Installation and Troubleshooting manual EK 410AB MG DEC Technical article Ultrix 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 VMScluster Systems October 1993 AA Q1X7A TE Dual Host MicroVAX Systems VAXcluster Systems Quorum February 1990 EC P0623 57 pp 3 31 VAX 4000 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 000References edit Digital Storage Systems Interconnect Gordon Bell Retrieved from https en wikipedia org w index php title Digital Storage Systems Interconnect amp oldid 1220784349, wikipedia, wiki, book, books, library,
