From: Bruce Momjian <bruce@momjian.us>
Message-Id: <201008131817.o7DIH1b03550@momjian.us>
Subject: Re: Advice configuring ServeRAID 8k for performance
In-Reply-To: <4C5B139B.2010600@2ndquadrant.com>
To: Greg Smith <greg@2ndquadrant.com>
Date: Fri, 13 Aug 2010 14:17:01 -0400 (EDT)
CC: Kenneth Cox <kenstir@gmail.com>, pgsql-performance@postgresql.org
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Greg Smith wrote:
> > 2) Should I configure the ext3 file system with noatime and/or 
> > data=writeback or data=ordered?  My controller has a battery, the 
> > logical drive has write cache enabled (write-back), and the physical 
> > devices have write cache disabled (write-through).
> 
> data=ordered is the ext3 default and usually a reasonable choice.  Using 
> writeback instead can be dangerous, I wouldn't advise starting there.  
> noatime is certainly a good thing, but the speedup is pretty minor if 
> you have a battery-backed write cache.

We recomment 'data=writeback' for ext3 in our docs:

	http://www.postgresql.org/docs/9.0/static/wal-intro.html
	
	Tip:  Because WAL restores database file contents after a crash,
	journaled file systems are not necessary for reliable storage of the
	data files or WAL files. In fact, journaling overhead can reduce
	performance, especially if journaling causes file system data  to be
	flushed to disk. Fortunately, data flushing during journaling can often
	be disabled with a file system mount option, e.g. data=writeback on a
	Linux ext3 file system. Journaled file systems do improve boot speed
	after a crash. 

Should this be changed?

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +