Horton

Re: file system and raid performance

Greg Smith <gsmith@gregsmith.com>

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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>, Scott Marlowe <scott.marlowe@gmail.com>, "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Date: 2008-08-08T22:30:07Z
Lists: pgsql-performance 
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