From: Bruce Momjian <bruce@momjian.us>
Message-Id: <201008170131.o7H1VPc26427@momjian.us>
Subject: Re: Advice configuring ServeRAID 8k for performance
In-Reply-To: <5687A8AD-CA70-4272-A32C-6AE5F491CEA4@richrelevance.com>
To: Scott Carey <scott@richrelevance.com>
Date: Mon, 16 Aug 2010 21:31:25 -0400 (EDT)
CC: Greg Smith <greg@2ndquadrant.com>, Kenneth Cox <kenstir@gmail.com>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
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Scott Carey wrote:
> Don't ever have WAL and data on the same OS volume as ext3.
> 
> If data=writeback, performance will be fine, data integrity will be ok
> for WAL, but data integrity will not be sufficient for the data
> partition.  If data=ordered, performance will be very bad, but data
> integrity will be OK.
> 
> This is because an fsync on ext3 flushes _all dirty pages in the file
> system_ to disk, not just those for the file being fsync'd.
> 
> One partition for WAL, one for data.  If using ext3 this is essentially
> a performance requirement no matter how your array is set up underneath.

Do we need to document this?

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

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