Subject: Re: Postgresql Performance on an HP DL385 and
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Steve Poe <steve.poe@gmail.com>
Cc: "Jim C. Nasby" <jnasby@pervasive.com>,
	Luke Lonergan <LLonergan@greenplum.com>,
	Alex Turner <armtuk@gmail.com>, pgsql-performance@postgresql.org
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	<721b21dc0608082245u6ee62e7dg522ff18e4d72683@mail.gmail.com>
	<20060809210539.GR40481@pervasive.com>
	<721b21dc0608091411g3a1a6e60q449de0d91020f9dc@mail.gmail.com>
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Date: Wed, 09 Aug 2006 16:37:28 -0500

On Wed, 2006-08-09 at 16:11, Steve Poe wrote:
> Jim,
> 
> I'll give it a try. However, I did not see anywhere in the BIOS
> configuration of the 642 RAID adapter to enable writeback. It may have
> been mislabled cache accelerator where you can give a percentage to
> read/write. That aspect did not change the performance like the LSI
> MegaRAID adapter does. 

Nope, that's not the same thing.

Does your raid controller have batter backed cache, or plain or regular
cache?  write back is unsafe without battery backup.

The default is write through (i.e. the card waits for the data to get
written out before acking an fsync).  In write back, the card's driver
writes the data to the bb cache, then returns on an fsync while the
cache gets written out at leisure.  In the event of a loss of power, the
cache is flushed on restart.