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From: MHJohnson@HI-MULTICS.ARPA (Mark Johnson)
Newsgroups: mod.computers.vax
Subject: Re: CI (Cluster) I/O
Message-ID: <870124003834.219026@HI-MULTICS.ARPA>
Date: Fri, 23-Jan-87 19:38:00 EST
Article-I.D.: HI-MULTI.870124003834.219026
Posted: Fri Jan 23 19:38:00 1987
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  Looking at the DECNET documentation for the CI connection indicates
that it is SLOWER to transfer data w/ DECNET on the CI than through the
ethernet.  A lot of stuff about extra overhead due to the smaller packet
size.  I would first look at increasing the buffer sizes on the ethernet
instead.  One way (if you can get agreement across the net...)  to do it
is to increase the buffer size and segment buffer size with NCP.  Our
systems had the lower limit (576) instead of the more reasonable
ethernet limit (1498).  This increases throughput quite a bit but must
be coordinated across the net.  See page 3-18 of the Networking Manual
for more information about adjusting the size.

Of course, you could have code running on both CPU's that talk their own
protocol across the ethernet as well.  The device driver book has the
details about that too.  About CPU to CPU transfers w/ the CI, I have no
idea how that works but I would start looking at the MSCP served disk
code to see what VMS does and copy that.  Good Luck!
  --Mark