info-vax@ucbvax.ARPA (08/16/85)
From: Thomas J. Linscomb <linscomb@ut-ngp.ARPA> > From: ken@CIT-Hamlet.ARPA > Subject: Duel path DSA devices > To: info-vax@CIT-Hamlet.ARPA > > I've read that you can have two HSC50s serving the same DSA disk > (for redundancy, only one HSC does the work at any one time). Has anyone > tried to connect the second port of an HSC50 served disk to the UDA-50 > on one of the cluster vaxes? Presumably you'd need to set the allocation > class the same and prey (or otherwise coerce) that the HSC50 was used as > the primary path. I'm interested in this principally for robustness > since we have been having trouble with our HSC50 (Circuit breaker in the > back trips occasionally). > -Ken Adelman > Caltech By design, dual porting a UDA disk does not work. But I have sat with someone at DECUS who had a system stay up after the HSC-50 serving the system disk went away and it continued to run on the UDA-50. Some people are lucky. Remember all the smarts they put out in the UDA-50? What happens to all those buffers and caches when you dual port the UDA? They screw you around! As a note, I have heard that this is on Digital's wish list (reference March 1983 PAGESWAPPER, p 18). Also this does not prevent you from using the UDA as a hot backup for the HSC. --Thomas aka linscomb@ut-ngp The University of Texas Computation Center