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Re: RAID Groups and ASM - I've got a problem, I think

From: Murching, Bob <>
Date: Tue, 6 Dec 2005 06:39:56 -0500
Message-ID: <>

More specific to the original poster's question, have you broken out navisphere analyzer to see what the CX is doing?

 -----Original Message-----

From: 	Niall Litchfield []
Sent:	Tue Dec 06 05:37:07 2005
Cc:	Oracle_L
Subject:	Re: RAID Groups and ASM - I've got a problem, I think

Are they duplicating the redundancy of the RAID system by using ASM redundancy as well? In my view if you are using ASM with LUNs on a SAN or other volume manager, you are better off declaring the redundancy as EXTERNAL for the disk groups. You also mention Dell 2850s in the plural, is this a RAC database? If so you'll get some other IO overhead (though not much IME) from that alone.  

Finally we found issues with firmware and driver versions with fibre attached storage (though we run Windows and different hardware so clearly it isn't a straight comparison, just another thing to consider.    

On 12/5/05, David Barbour < > wrote:

Looking into a performance problem on RHEL 3.0 AS QU4 running on Dell 2850s with 8gB RAM and dual 3.6gHz PIV processors and a fibre-attached EMC CX-500.

A simple 100000 row insert on an identical database running on a Windoze XP desktop with 1gB RAM and internal IDE drives takes 137 seconds. On the Linux box it takes 443 seconds!

They're using ASM, and there's one diskgroup defined for the DB, that has six LUNS from four different RAID Groups on the SAN. I think the intent of the folks who installed it was to try to spread the IO across as many spindles as possible (laudable goal), but I don't think using ASM to to that is the best solution.

Might I not have an issue with the overhead of striping across four different RAID Groups? When I run the insert, the cpu on the box never goes above 5% or so, but IO Waits are in the 60 - 70% range. I't's the only activity happening on the box , period. To make it somewhat worse, the numbers of LUNS from each RAID Group aren't consistent ( 2 from RG0, 2 from RG1, 1 from RG4 and 1 from RG5) and the sizes, although not radically different, aren't identical. The LUNS from RG1 are 150M vs. 166M for RG2/4/5.

I really don't think ASM was designed (at least at this point - to stand in as a substitute for metaluns at the storage level.

Any thoughts?  


Niall Litchfield
Oracle DBA
-- Received on Tue Dec 06 2005 - 05:42:08 CST

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