Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!ccu.umanitoba.ca!herald.usask.ca!skorpio!dzubin
From: dzubin@skorpio.Usask.ca (SED's Thomas Dzubin)
Newsgroups: comp.sys.dec
Subject: 'real' speed of SCSI vs. SDI vs. DSSI
Message-ID: <1991Jan25.204122.18983@herald.usask.ca>
Date: 25 Jan 91 20:41:22 GMT
Sender: dzubin@skorpio.USask.Ca
Reply-To: dzubin@skorpio.USask.Ca (SED's Thomas Dzubin)
Organization: University of Saskatchewan
Lines: 31
Nntp-Posting-Host: skorpio.usask.ca


Please excuse the silly questions from a hardware-ignorant system manager:

We are currently looking at replacing our (very) aging VAX 11/750 with
something else DEC-like to be a VAXcluster boot node and central storage
place for other satellite nodes.  Now, I could be cheap and get a uVAX 3100
with a couple Gig. of SCSI disk, but if I look at the Systems and Options
catalogs that DEC puts out, I find that the MAX I/O throughput for SCSI
on the 3100 is 1.5 MB/s.  If I wanted to spend a bit more money and go
to something Q-bus based in the 3xxx series like a 3400, I could get
4 MB/s on DSSI disks.

Now, obviously on the boot node of a cluster, I want to get the most disk
throughput, rather than raw CPU speed, right?
(In my Sys & Opt. catalog the 3100 is rated @ 3.5 VUPS and the 3400 is 2.4)

Obviously, there are other factors such as expandability and bus vs. non-bus
computers...

...but...

THE QUESTION IS: am I right in saying that the SCSI interface is a major
bottleneck making the 3100 a poor choice for a boot node in a small cluster??

My dilemma: I can buy one 3400 or I can buy four 3100s...what to do?

Thomas Dzubin
SED Systems Inc.  #18 Innovation Boulevard, Saskatoon Saskatchewan, Canada
dzubin@skorpio.usask.ca
"Network Coordinator" (whatever that means)
(306) 933-1573