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From: Greg Smith <gsmith@gregsmith.com>
To: Mark Mielke <mark@mark.mielke.cc>
Cc: Andrej Ricnik-Bay <andrej.groups@gmail.com>
Cc: Scott Marlowe <scott.marlowe@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: file system and raid performance
Date: Fri, 8 Aug 2008 18:30:07 -0400 (EDT)
Message-ID: <Pine.GSO.4.64.0808081809430.21924@westnet.com> (raw)
In-Reply-To: <489B727B.6010800@mark.mielke.cc>
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	<b35603930808071457x40334261uad77dab2623f2757@mail.gmail.com>
	<489B727B.6010800@mark.mielke.cc>

On Thu, 7 Aug 2008, Mark Mielke wrote:

> Now, modern Linux distributions default to "relatime"

Right, but Mark's HP test system is running Gentoo.

(ducks)

According to http://brainstorm.ubuntu.com/idea/2369/ relatime is the 
default for Fedora 8, Mandriva 2008, Pardus, and Ubuntu 8.04.

Anyway, there aren't many actual files involved in this test, and I 
suspect the atime writes are just being cached until forced out to disk 
only periodically.  You need to run something that accesses more files 
and/or regularly forces sync to disk periodically to get a more 
database-like situation where the atime writes degrade performance.  Note 
how Joshua Drake's ext2 vs. ext3 comparison, which does show a large 
difference here, was run with the iozone's -e parameter that flushes the 
writes with fsync.  I don't see anything like that in the DL380 G5 fio 
tests.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD



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