Subject: Re: [PERFORM] Arguments Pro/Contra Software Raid
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Steve Atkins <steve@blighty.com>,
	PostgreSQL General <pgsql-general@postgresql.org>,
	"Pgsql-Performance ((E-mail))" <pgsql-performance@postgresql.org>
In-Reply-To: <200605100102.k4A12wa12853@candle.pha.pa.us>
References: <200605100102.k4A12wa12853@candle.pha.pa.us>
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Date: Wed, 10 May 2006 09:42:59 -0500

On Tue, 2006-05-09 at 20:02, Bruce Momjian wrote:
> Scott Marlowe wrote:
> > Actually, in the case of the Escalades at least, the answer is yes. 
> > Last year (maybe a bit more) someone was testing an IDE escalade
> > controller with drives that were known to lie, and it passed the power
> > plug pull test repeatedly.  Apparently, the escalades tell the drives to
> > turn off their cache.  While most all IDEs and a fair number of SATA
> > drives lie about cache fsyncing, they all seem to turn off the cache
> > when you ask.
> > 
> > And, since a hardware RAID controller with bbu cache has its own cache,
> > it's not like it really needs the one on the drives anyway.
> 
> You do if the controller thinks the data is already on the drives and
> removes it from its cache.

Bruce, re-read what I wrote.  The escalades tell the drives to TURN OFF
THEIR OWN CACHE.