From:	MERC::"uunet!CRVAX.SRI.COM!RELAY-INFO-VAX"  5-NOV-1992 09:09:08.51
To:	info-vax@kl.sri.com
CC:	
Subj:	RE: SCSI and /or SCSI-Multihost-Cluster ??

Bruno Egger of egger@mpi-fg-koeln.mpg.dbp.de writes:

>we are planning to realize a SCSI-Cluster in the near future. We want to
>connect our 2 Vaxstations 3100 Modell 30 and 38 via a CMD-
>Multihostadapter. Therefore i've got the following questions:

Digital doesn't currently support clustering over the SCSI bus. What you would
need is an SCS port driver to communicate between the systems, which doesn't
currently exist (at least outside of Digital - no doubt they've tried it).

The port drivers currently supported for clustering over busses are:
	PADRIVER	"CI type" ports, e.g., CI, DSSI, where the port is 
			intelligent, and can directly access system memory
	PBDRIVER	BVP port (BI VAX port) Used for BI systems with a CI,
			or disk or tape attached to the BVP
	PEDRIVER	Ethernet ports

There are also SCS port drivers for communicating to local devices:
	PIDRIVER	KFQSA port (DSSI controller on a Qbus)
	PUDRIVER	UQSSP ports (Unibus, Qbus Storage Systems Port, e.g.
			RQDX3), with disk drives, where the driver fakes out SCS
	PTDRIVER	UQSSP ports, with tape drives, again the driver fakes 
			out SCS

I can tell you from experience, that writing an SCS port driver is one of the
most difficult tasks you are ever likely to encounter.

If CMD provides you with an SCS port driver, then things will probably work,
though I haven't heard that they've done this.



Brian Catlin, Closed Loop Control, Inc., VMS Internals Consultants
"Why do we need UNIX [eunuchs] ?  We don't even have a harem"