Subject: Re: RAID stripe size question
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Ron Peacetree <rjpeace@earthlink.net>
Cc: PG Performance <pgsql-performance@postgresql.org>
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Date: Tue, 18 Jul 2006 14:48:46 -0500

Nope, haven't tried that.  At the time I was testing this I didn't even
think of trying it.  I'm not even sure I'd heard of RAID 50 at the
time... :)

I basically had an old MegaRAID 4xx series card in a dual PPro 200 and a
stack of 6 9 gig hard drives.  Spare parts.  And even though the RAID
1+0 was relatively much faster on this hardware, the Dual P IV 2800 with
a pair of 15k USCSI drives and a much later model MegaRAID at it for
lunch with a single mirror set, and was plenty fast for our use at the
time, so I never really had call to test it in production.

But it definitely made our test server, the aforementioned PPro200
machine, more livable.

On Tue, 2006-07-18 at 14:43, Ron Peacetree wrote:
> Have you done any experiments implementing RAID 50 this way (HBA does RAID 5, OS does RAID 0)?  If so, what were the results?
> 
> Ron
> 
> -----Original Message-----
> >From: Scott Marlowe <smarlowe@g2switchworks.com>
> >Sent: Jul 18, 2006 3:37 PM
> >To: Alex Turner <armtuk@gmail.com>
> >Cc: Luke Lonergan <llonergan@greenplum.com>, Mikael Carneholm <Mikael.Carneholm@wirelesscar.com>, Ron Peacetree <rjpeace@earthlink.net>, pgsql-performance@postgresql.org
> >Subject: Re: [PERFORM] RAID stripe size question
> >
> >On Tue, 2006-07-18 at 14:27, Alex Turner wrote:
> >> This is a great testament to the fact that very often software RAID
> >> will seriously outperform hardware RAID because the OS guys who
> >> implemented it took the time to do it right, as compared with some
> >> controller manufacturers who seem to think it's okay to provided
> >> sub-standard performance. 
> >> 
> >> Based on the bonnie++ numbers comming back from your array, I would
> >> also encourage you to evaluate software RAID, as you might see
> >> significantly better performance as a result.  RAID 10 is also a good
> >> candidate as it's not so heavy on the cache and CPU as RAID 5. 
> >
> >Also, consider testing a mix, where your hardware RAID controller does
> >the mirroring and the OS stripes ((R)AID 0) over the top of it.  I've
> >gotten good performance from mediocre hardware cards doing this.  It has
> >the advantage of still being able to use the battery backed cache and
> >its instant fsync while not relying on some cards that have issues
> >layering RAID layers one atop the other.
>