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From: info-vax@ucbvax.ARPA
Newsgroups: fa.info-vax
Subject: Re: High speed data acquisitions to RA disks
Message-ID: <7595@ucbvax.ARPA>
Date: Thu, 30-May-85 09:51:08 EDT
Article-I.D.: ucbvax.7595
Posted: Thu May 30 09:51:08 1985
Date-Received: Fri, 31-May-85 04:03:40 EDT
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Organization: University of California at Berkeley
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From: ulysses!mhuxr!mhuxt!houxm!hou2d!afb3@BERKELEY

I used to achieve approx. 300k bytes/sec on an RM02 (32 sectors
per track, 2400 RPM) with abuffer size of 8192-16384 bytes and using
FCS block I/O (not QIO's!!!!!).  The result is read one buffer (in
one revolution), miss a revolution, read one buffer).  This assumes
that the "real-time" I/O is the only activity on the disk, the file
is preallocated and contiguous, and NOWRITECHECK is enabled.  These
assumptions cause the head arm to be on track/on cylinder after the
first I/O, with only track to track seeks as we go.

The RM02, however, is an ordinary, vanilla, normal type disk.  The
RA80/60/81's have a different layout and "automatically" relocate
bad sectors.  Good for systems, bad for realtime....  The killer is
the transparent seeks that might occur.  Also, even if the controller
does it, writecheck will killyou everytime....

If you are running standalone and with WRITECHECK disabled, you
might try different packs in you RA60 or allocate different files
on the same disk and try them...(using different LBN's on the disk
should cause different bad block mapping by the UDA..)

One more thought.  If you contend with one (1!!!) other task doing
I/O on the disk, your effective thoughput would drop to the 100K+
level.  (avg. seek + avg. latency + read/write time)/2.....  You
get one I/O, he gets one, you get one, he gets one... Sicking isn't
it.

I played with this nonsense for 5 years on an 11/55 with great
success (and alot of fun!!) doing large (2k X 2k) matrix problems.
It works like a camp if the controller doesn't out smart you.


Al Baldwin
AT&T-Bell Labs
...!ihnp4!hou2d!afb3


[These opinions are my own....Who else would want them!!!]