Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!nrl-cmf!ames!pasteur!ucbvax!decwrl!sun!pitstop!sundc!seismo!uunet!portal!cup.portal.com!Mike_W_Ryan
From: Mike_W_Ryan@cup.portal.com
Newsgroups: comp.sys.hp
Subject: Re: Disc Cacheing
Message-ID: <8626@cup.portal.com>
Date: 1 Sep 88 00:40:45 GMT
References: <9@raider.UUCP>
Organization: The Portal System (TM)
Lines: 23
XPortal-User-Id: 1.1001.2836

Regarding the inquiry on disc caching on a S70.

Your problem probably stems from the following:

1) locality of data on ldev 1- use LOGAUDIT or HPTREND to identify
   the files that are hit on ldev alot. Since it is a 571 mb drive
   this could take some digging. many systems benefit from using a
   smaller disc on ldev 1 like a 7936 or 7920/25 even to prevent
   data sets from getting on ldev 1. If you find any suspect files, you
   can just store them, then restore with the "DEV=" parm.
2) Things aren't as bad as you think. The "official" guideline used
   by HP to identify systems that are benefitig from cacheing is:
   a) read hit > 75%
   b) ratio of reads/write approx 3:1

You are getting something out of caching for sure. 69% reduction is actually
pretty good. If you haven't already, you might wan't to try turning
BLOCKONWRITE= ON. This usually reduces the number of writes "lined up"
behind another write to disc since the writes will then happen at
the processes priority rather than background priority at first.

Last of all, the way your application performs may be partly
responsible, but that remains a constant in most shops.