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From: LEICHTER-JERRY@YALE.ARPA
Newsgroups: comp.os.vms
Subject: Re: Local-Area VAXclustering.
Message-ID: <8707210930.AA02360@ucbvax.Berkeley.EDU>
Date: Tue, 21-Jul-87 05:30:34 EDT
Article-I.D.: ucbvax.8707210930.AA02360
Posted: Tue Jul 21 05:30:34 1987
Date-Received: Wed, 22-Jul-87 06:26:48 EDT
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    	We here at the University of Rhode Island are trying to review our
    options for increasing the overall performance of our VAX 11/780.  One
    idea brought up was to LAV the 780 to multiple uVAX IIs.  What exactly
    does this buy us?

It buys your more CPU power.  The resulting system is suitable for multi-
stream applications in which dynamic load balancing is not an issue.  That
is:  You will be able to spread users and jobs across a number of CPU's, so
if your system is loaded up because it always has several jobs running at
once, you'll win.  No one job will, in and of itself, run any faster (except
for lack of competition with other jobs); and once a job is created, it has
to stay on the system it was created on.  The 780, since it will serve all
the disks to the LAVC, will continue to be a single point of failure - you
won't gain here.

		       Can we set up terminal servers to share the 780 and
    uVAXs just as we would for a normal cluster of 780s?  Can we share disks
    and have one common SYSUAF.DAT?  We've got three RM05s and one RA81 that
    we'd like to share across systems.

Yes to both of these.  The LAVC software is identical to "big cluster" soft-
ware except at the very lowest levels, where it uses the Ethernet instead of
the CI.

Note that disk accesses from the uVAXes will be somewhat slower than equiva-
lent access on the 780, though not by all that much.  Since you are talking
about uVAXes, not VAXStations, you'll certainly have local disks; putting
swapping an paging files on them will help.  You can put other stuff there,
too, and even serve the local disks to the cluster.

There will be some load on the 780 from serving the micros.  How much depends
on how many micros you will have.  You should experiment, but with more than
a couple of micros, your best configuration may be to not use the 780 for
interactive jobs at all - reserve it for disk serving and batch jobs.

(A configuration like this really brings home the advances in this field.
The 780 "feels" like the big machine in the configuration, but in fact it's
no faster and probably has about the same amount of memory as the micros.  The
only way in which it's "big" is in available I/O bandwidth, and the use of
that bandwidth in faster, bigger disks.)
							-- Jerry
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