Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!lll-crg!nike!ucbcad!ucbvax!hplabs!sdcrdcf!trwrb!desint!geoff
From: geoff@desint.UUCP (Geoff Kuenning)
Newsgroups: net.unix-wizards
Subject: Re: RAM disk vs paging + buffer cache
Message-ID: <244@desint.UUCP>
Date: Thu, 14-Aug-86 03:01:20 EDT
Article-I.D.: desint.244
Posted: Thu Aug 14 03:01:20 1986
Date-Received: Sun, 17-Aug-86 05:32:11 EDT
References: <514@opus.nbires.UUCP> <240@whuxcc.UUCP>
Reply-To: geoff@desint.UUCP (Geoff Kuenning)
Organization: SAH Consulting, Manhattan Beach, CA
Lines: 27

In article <240@whuxcc.UUCP> judah@whuxcc.UUCP (Judah Greenblatt) writes:

>   I'm not
>   sure why, but it seems that the following sequence generates several
>   physical I/O operations, even when the buffer-cache is empty:
> 	- create a file
> 	- write 1 block of data
> 	- close it

This is an unfortunate side effect of the file system reliability
enhancements that were done for System V (III?).  This is the unfortunate
reality of reliability--it trades off against performance.  In this case,
whenever an "important" change is made to an i-node, it is written to
disk immediately.  I believe this also applies to directories.  It has
a negative effect on performance in several ways, but most users seem
to feel the reliability is worth it.

> -  One thought on why you might not want to let the block buffers
>    do all the work: can you imagine what a 'sync' would
>    cost on a system with 20,000 block buffers?

Also, can you imagine what it would be like to crash WITHOUT sync-ing on a
system with 20,000 block buffers?  Even with the reliabiltiy enhancements?
-- 

	Geoff Kuenning
	{hplabs,ihnp4}!trwrb!desint!geoff