From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Mason <mason@suse.com>
Subject: Re: data-logging on top of linux-2.4.19p7-compound-speedup-2.patch
Date: 20 May 2002 09:46:09 -0400
Message-ID: <1021902370.22608.17.camel@tiny>
References: <200205040219.42912.Dieter.Nuetzel@hamburg.de>
	<1020608683.1510.1353.camel@tiny> 
	<200205172204.22469.Dieter.Nuetzel@hamburg.de>
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To: Dieter =?ISO-8859-1?Q?N=FCtzel?= <Dieter.Nuetzel@hamburg.de>
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On Fri, 2002-05-17 at 16:04, Dieter N=FCtzel wrote:

> So data=3Djournal is very slow for me.
> What's wrong?

Nothing ;-)  data=3Djournal writes every data block twice, opnce to the
log and once to the main disk.  Most of the time this makes things
roughly 1/2 as fast as it was before.

The only time data=3Djournal helps is when you've got a very fsync or
O_SYNC heavy application.  Try running iozone with -o on both
data=3Djournal and without it, data=3Djournal is 2 or 3 times as fast.

This is because we can do the sync by writing to the log instead of
writing to the log and having to seek back to the main disk.

-chris