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From: haahr@polygen.uucp (Paul Haahr)
Newsgroups: comp.unix.wizards
Subject: Re: How many packets per second from a Sun-3 file server?
Message-ID: <10@polygen.UUCP>
Date: Wed, 12-Aug-87 09:06:15 EDT
Article-I.D.: polygen.10
Posted: Wed Aug 12 09:06:15 1987
Date-Received: Fri, 14-Aug-87 05:24:45 EDT
References: <2820@phri.UUCP> <13745@topaz.rutgers.edu>
Reply-To: haahr@polygen.UUCP (Paul Haahr)
Organization: Polygen Corporation, Waltham, MA
Lines: 34
Summary: memory on a file server and kernel buffers

In article <13745@topaz.rutgers.edu>,
	hedrick@topaz.rutgers.edu (Charles Hedrick) writes:
...
>By the way, we understand that some people are using 8MB machines as
>file servers.  Does anyone have any evidence that adding memory helps
>performance, for a machine used only as a file server?  When people
>add memory, do they also retune the kernel so that it uses more
>memory for block I/O buffers?  (If not, most of that extra memory
>will be allocated for user processes, of which there are presumably
>none.)

With a sun-3/180 with one eagle and 12M acting almost entirely as an nd
(both boot and swap) server, the feel (sorry about no more quantitative
a result) of the machines (all 3/50s) running off of it improved a lot
after we increased the number of buffers from 10% of memory (the Berkeley
and Sun default) to 920 pages (920 pages * 8k/page ~ 60% * (12M - kernel))
Note that this machine does almost no NFS work; that is handled by a second
server.

We have not tried this yet for the NFS server.  I'm not sure what the
ramifications of tuning the server this way are since nfsd and biod are
"kernel processes that have user context." (paraphrased from nfssvc(2))
I would guess that the same tuning would have a similar effect, but haven't
had a chance to try it.

SunOS 4.0 and the new virtual memory subsystem (Gingell et al, Usenix 1987)
should improve the system, in that we won't need to set aside a specific
portion of our memory to be used for block i/o buffers.  One gripe that
will disappear when kernel buffers disappear is that as a non-source site
we can't tune this number except by using adb, and therefore the information
is not recorded in our /sys/conf files.
-- 
paul haahr				(bu-cs|princeton)!polygen!haahr
polygen corporation, waltham, ma	617-890-2888