Re: Oracle Performance - RAID vs split tables

Please visit this site for more info on RAID

 http://www.ipass.net/~davesisk/oont_availability_raid.htm

Messages received from my posting on this subject. I am grateful for their valuable contributions. They provided me foundations for my choices.

1)
From: Julio Negueruela <julio.negueruela_at_si.unirioja.es> Organization: Universidad de La Rioja

My personal experience: RAID 5 is not good for databases with a long number of transactions. If this is not your scenario it's a reasonable way of implementing. Anyway, I strongly recommend you to allocate the online and archive logs, index tablespaces and may be too the temp tablespaces in separated disks (RAID 1 for indexes and 0 for temp, for example)

2)
From: cpereyra_at_ix.netcom.com

My understanding is that Raid 0+1 (striping and mirroring) is best for performance and the most expensive. Raid 5 is OK but suffers from some performance penalty during writes. I am sure that you are going to get a lot of advice on this subject, so for the next person, if you know the answer could you explain the difference between 0+1 and 1+0? I know that one is preferred over the other but not sure how or why.

3)
From: jason_at_seahorse.demon.co.uk (Jason Salter)

Imagine you had 10 discs, you could stripe the first 5 and then mirror them (Raid 0+1). Or you could mirror 5 disks and then create a stripe across the mirrors (Raid 1+0).

With Raid 0+1, you could lose up to two disks (one from each stripe set) before your system would go down (assuming you have no hot swaps).

With Raid 1+0, you could lose up to six disks (one from each mirror pair) before your system would collapse.

4)
From: Martin Hepworth <maxsec_at_usa.net>

Well I'm doing similar and am about to test various combinations...right now I'm going for 2x RAID5 sets, 1 for the data and 1 for the redo logs. With the 5200 you have hardware RAID5 so writing should be nice and fast, not that much different from 0+1, and RAID 0+1 is probably not justifiable for extra tiny perf gain agianst cost of disks.

5)
From: "Alan D. Moorman" <alm2_at_dss.state.va.us> [Add to Address Book]

I recently took the Oracle8 Perf & tuning class in which the instructor said "Never, ever put your redo logs on Raid5!" Since this is the single most IO-intensive part of Oracle, it's a really bad idea....unless you're implementing a DW application where it really doesn't matter.

I personally prefer mirroring without striping. If you're going to mirror at OS level, don't bother with multiple redo log members (it's redundant).

Raindrop Support wrote:

> Can anyone shed any light on a performance choice?
>
> Many of our customers are worried about disk crashes and the resulting data
> loss so RAID is an obvious solution. We normally recommend hardware RAID5.
>
> However, we have recently been advised by various Oracle gurus that it is
> better for Oracle performance to manually split up the physical locations of
> individual tables, indices and logs across physical disks. This cannot be
> done with RAID. Additionally, we have been advised that RAID5 actually
> *slows down* Oracle.
>
> Any comments?
>
> Replies to newsgroup please.

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Breno de Avellar Gomes
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