To: Steve Atkins <steve@blighty.com>
Cc: PostgreSQL General <pgsql-general@postgresql.org>,
	"Pgsql-Performance ((E-mail))" <pgsql-performance@postgresql.org>
Subject: Re: Arguments Pro/Contra Software Raid
References: <e3pmkc$12mk$1@news.hub.org>
	<473FC220-A52C-4954-81E9-A14ED33164C2@blighty.com>
In-Reply-To: <473FC220-A52C-4954-81E9-A14ED33164C2@blighty.com>
From: Greg Stark <gsstark@mit.edu>
Organization: The Emacs Conspiracy; member since 1992
Date: 10 May 2006 00:50:28 -0400
Message-ID: <87zmhqwkiz.fsf@stark.xeocode.com>
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Steve Atkins <steve@blighty.com> writes:

> On May 9, 2006, at 2:16 AM, Hannes Dorbath wrote:
> 
> > Hi,
> >
> > I've just had some discussion with colleagues regarding the usage  of
> > hardware or software raid 1/10 for our linux based database  servers.
> >
> > I myself can't see much reason to spend $500 on high end controller  cards
> > for a simple Raid 1.
> >
> > Any arguments pro or contra would be desirable.

Really most of what's said about software raid vs hardware raid online is just
FUD. Unless you're running BIG servers with so many drives that the raid
controllers are the only feasible way to connect them up anyways, the actual
performance difference will likely be negligible.

The only two things that actually make me pause about software RAID in heavy
production use are:

1) Battery backed cache. That's a huge win for the WAL drives on Postgres.
   'nuff said.

2) Not all commodity controllers or IDE drivers can handle failing drives
   gracefully. While the software raid might guarantee that you don't actually
   lose data, you still might have the machine wedge because of IDE errors on
   the bad drive. So as far as runtime, instead of added reliability all
   you've really added is another point of failure. On the data integrity
   front you'll still be better off.


-- 
Greg