(no subject)

David,

I don't think having two LUN's on the same RAID system was a wise decision. 
Contention is introduced this way on the same physical devices.

Goran


Date: Mon, 5 Dec 2005 10:53:22 -0800 (PST)
From: David Barbour <david.barbour@xxxxxxxxxxxxx>
Subject: RAID Groups and ASM - I've got a problem, I think

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 - 10.1.0.4) to stand in as a substitute for metaluns at the storage level.
Any thoughts?

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