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From: info-vax@ucbvax.ARPA
Newsgroups: fa.info-vax
Subject: Re: Unibus Disks
Message-ID: <3249@ucbvax.ARPA>
Date: Tue, 13-Nov-84 13:01:21 EST
Article-I.D.: ucbvax.3249
Posted: Tue Nov 13 13:01:21 1984
Date-Received: Thu, 15-Nov-84 01:46:59 EST
Sender: daemon@ucbvax.ARPA
Organization: University of California at Berkeley
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From: lhasa!stew@harvard.ARPA

The hypothetical question that you pose is impossible to answer.  The Eagle
and RA81/UDA50 configurations have quite different characteristics, and the
answer is heavily dependant on the type of job you are running.

The advantage of the UDA50 is that it does quite a lot of optimization:
seek ordering, rotational latency, buffering, etc.  In an environment
which consisted of, say, several heavy page fault bound processes (for
example, large lisp or other GC-based systems) this optimization will
have a large effect.  In other environments (say, database applications)
which do larger bursts, the cpu-controller interface becomes the bottleneck
and the Eagle/Massbus emulator configuration wins.

The above is probably still a simplification.  Furthermore, this neglects
the single-vendor shop advantage when it comes to Field Service.  And finally,
does anyone know how long software updates for foreign controllers lag behind
the releases from DEC?  This last may only be meaningful for VMS;  I don't
know what AT&T's and Berkeley's policies are on this.  You also don't say
how much service will be done by locally trained techs and how much you
will rely on DEC Field Service.  How far away is the SI office?

Is there really no cost difference?  The monthly maintenance on the RA81's
is amazingly low.  Be sure to take that into account.

For my setup, a number of large page-fault bound jobs at an otherwise
all-DEC VMS site, the UDA50/RA81 combo was the clear choice.  However,
anyone who answers your query in 25 words or less is not answering it
for you, they are answering it for them.

Stew Rubenstein
Harvard Chemistry