info-vax@ucbvax.ARPA (11/14/84)
From: lou@aero3 (Lou Nelson (ISRO)) >Date: 12 Nov 1984 1252-PST (Monday) >To: Bill Mitchell <whm%arizona.csnet@csnet-relay.ARPA> >Cc: info-vax@sri-csl.ARPA >Subject: Re: 8600 performance? > >Yeah, I have been puzzled by the emphasis on UNIBUS stuff myself. >I asked a few DEC people about why they put an RA81, which is a >fine drive, which is a 2MB/s device, on a .5-.8MB/s UNIBUS. >They said that those drives are part of the DSA and they want you >to use the CI bus and cluster them together, and that the CI >bus is 70 Mb/s and isnt unibus bound. But then I pointed out that >their file server, a HSC50 is an 11-based product and has the unibus >in it as well, and the disks go thru an UDA50. I asked what the >difference was where the unibus bottleneck was, that its still >a bottleneck. They didnt know why, but they said they had a good >reason. Sigh. I really like the RA81, its a great idea, >but this unibus stuff is ridiculous. Thats why I only use >Eagles and Emulex massbus controllers (SI makes them too). >Surely they arent planning a new line of PDP11 unibus >products... I was puzzled about this about a year ago and asked a regional support guy and he pointed out that the data paths in the HSC50 involved very fast bit-slice processors and that the pdp11 was involved only in control. He didn't know if the horrendous disk drive port switching time was finessed though. I couldn't get the RA81s to work well and switched to SI 9900s and Eagles also.