Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uflorida!ufqtp!bernhold
From: bernhold@qtp.ufl.edu (David E. Bernholdt)
Newsgroups: comp.unix.cray
Subject: How to use an SSD?
Message-ID: <1019@orange19.qtp.ufl.edu>
Date: 29 May 90 02:39:06 GMT
Reply-To: bernhold@qtp.ufl.edu (David E. Bernholdt)
Organization: University of Florida Quantum Theory Project
Lines: 38


SSDs have been around on Crays for a long time.  I remember about 6
years ago working on a Cray (running CTSS) where you used the SSD as a
high-speed disk, but had to do some special things in the code to do
it -- system calls (my memory of the details is rather dim).  

I know SSDs are still around, but they don't seem to be used in the
same way any more.  I've poked around in the man pages, and there are
a few things related to SSDs, but not much.  I had always assumed that
the OS had been taught how to use the them & most of the stuff in the
man pages point in that direction.

On the other hand, in the Fall 1989 Cray Channels, there is an article
entitled "Designing effective out-of-core solutions" by Moshe Reshef,
which makes heavy use of SSDs -- apparently explicitly.  So now I've
become curious about a few things...

How are SSDs presently used (under UNICOS)?

It seems from the routines listed in the man pages that "extended main
memory" is the way to think of an SSD if one wishes to program for it
explicitly. From the article, though, they seem to be using a fast
disk model for it.  So how *do* you actually think of it?

Does anyone actually explicitly code for an SSD?  Is it worth it? 

Is explicitly coding for the SSD more or less efficient for the
particular program than letting the OS use the SSD as it wants?  How
about for the overall system performance (i.e. what is best in the
eyes of the people who own the Cray vs. what is best for a user who
just wants his program to run as-fast-as-possible for the least cost)?

Thanks in advance for helping satisfy my curiosity...
-- 
David Bernholdt			bernhold@qtp.ufl.edu
Quantum Theory Project		bernhold@ufpine.bitnet
University of Florida
Gainesville, FL  32611		904/392 6365