Re: DASD Disk Layout Advice

From: Noons <wizofoz2k_at_gmail.com>
Date: Wed, 25 Nov 2009 13:33:35 -0800 (PST)
Message-ID: <3bac7a00-bd9c-4472-8d5f-a9ff4fe59c72_at_g26g2000yqe.googlegroups.com>



On Nov 25, 2:18 pm, Pat <pat.ca..._at_service-now.com> wrote:

>
> The counterproposal is to just make one big raid group like:
>
> Disk 0..7 Raid 10
>
> What are folks doing these days with these bold 'old 300G disks? It
> seems supremely wasteful to use an entire 300G drive hold 20G worth of
> red.

Would you believe RAID 5? For most *sequential* workloads, it works perfectly and is as good as RAID1+0, besides being much more efficient in disk usage. Contrary to what most folks believe. But you'll need an odd number of disks so in your case 7 is the magic number. Leaves you a spare drive for the odd bits.
I hope that controller has multiple paths? Otherwise you're in serious I/O performance trouble...
So, what is "sequential" in an Oracle db server? Redo, SYSTEM, OS, software itself, archived redos, FRA. And unless you are trying to run the latest 10000000000 concurrent user OLTP benchmark-winning system in such a hardware configuration, I'd say your data and index areas will likely be mostly sequential I/ O.
Temp and Undo might not but then again it's highly contingent on the workload. If you have big serial updates the Undo will be mostly sequential in nature.
Temp is a different animal, it can be all kinds. But then again, you can't keep everyone happy! ;)

Note that by "sequential" I don't mean ordered! A FTS for example is an example of sequential. So is an index FFS, an unqualified update, a long batch insert, etcetc.
What is random? Lots and lots of queries and updates to a single row or a very small number of rows, in many tables.

> Any recommendations, advice, etc would be appreciated.

You got them. Pity you're not in Sydney, we're talking about precisely this at the Sydney Oracle Meetup this Friday evening: http://dbasrus.blogspot.com , bottom half. Received on Wed Nov 25 2009 - 15:33:35 CST

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