Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wotan!moxie!lobster!nuchat!steve
From: steve@nuchat.sccsi.com (Steve Nuchia)
Newsgroups: comp.unix.sysv386
Subject: Re: DPT controller?
Keywords: DPT disk controller
Message-ID: <1991May22.010734.15694@nuchat.sccsi.com>
Date: 22 May 91 01:07:34 GMT
References: <1991May14.235110.18644@tous.uucp> <1991May17.131717.26942@virtech.uucp> <31@metran.UUCP>
Distribution: na
Organization: South Coast Computing Services, Inc.  Houston
Lines: 26

In article <31@metran.UUCP> jay@metran.UUCP (Jay Ts) writes:
>I have been wondering under what conditions the DPT and other caching disk
>controllers are really effective enough to be worth the extra price and
...
>cache on the controller is only about 10-15%, even if it is maxed out at

In an ideal world (ie, one in which you have source) you can make
certain trade-offs in software, where they belong, and hardware hacks
like caching controllers become completely irrelevant.  Without the
ability to make those trade-offs in software, sometimes hardware
is the only answer.

In sysV there are a number of places where synchronous writes to
the disk are forced.  Number one on my personal list of pet peeves
is unlink(2), for instance.  Using a non-write-through caching controller
will make rm -rf /usr/spool/news run as fast as it should instead of
taking about 50 ms per article.

If you wanted to make the trade-off of non-synchrounous inode updates
for faster directory operations, and you don't have source, the only
way to do it is in hardware.  Depending on your jop mix it may be worth it.
-- 
Steve Nuchia	      South Coast Computing Services      (713) 964-2462
	"Innocence is a splendid thing, only it has the misfortune
	 not to keep very well and to be easily misled."
	    --- Immanuel Kant,  Groundwork of the Metaphysic of Morals