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From: pcg@aber-cs.UUCP (Piercarlo Grandi)
Newsgroups: comp.unix.xenix
Subject: Re: Caching disk controllers and 386 multiprocessor
Summary: Caching is best in main memory...
Keywords: multiprocessing, disk controller
Message-ID: <1013@aber-cs.UUCP>
Date: 13 Jun 89 15:57:07 GMT
Reply-To: pcg@cs.aber.ac.uk (Piercarlo Grandi)
Organization: Dept of CS, UCW Aberystwyth
	(Disclaimer: my statements are purely personal)
Lines: 25

In article <134@unifax.UUCP> sl@unifax.UUCP (Stuart Lynne) writes:
    
    It seems obvious that adding 2MB of buffers is going to help somewhat. 
    But where is the best place to put the memory, on the controller or in the 
    kernel?

Extensive research (on mainframes, mostly) shows that caching is better done
by the os in main memory. Also, it is vastly more flexible. Even more
important, caching controllers become married to their discs, and need (if
safety has any importance) battery backup of the cache.
    
    I get the impression from the articles I read that the reviewer simply puts
    in the caching controller steps back and marvels at the improved response
    :-)

Precisely, even reviewers are often just glorified naive users, and don't
bother twiddling the cache size. I remember reading that on a "tipical mini"
a unix buffer cache of 2 megs gives you a hit rate of almost 90%. Using large
buffer caches in NFS clients (25% of memory) *and* servers (I have configured
cache of up to 6 megs) cuts network traffic and clients response time
wonderfully.
-- 
Piercarlo "Peter" Grandi           | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcvax!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk