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Slice and dice a SAN box?

I got this SAN box with 6x450GB hard drives which I plan to support both Exchange and Oracle database.

I assume I should set up 2 RAID 5 with 3 hard drives each. Exchange will use one RAID array, and Oracle will use another one.

I should not set up 1 big RAID 5 with all 6 drives but divide the array to two logical disks, right?
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PaperTiger
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PaperTiger
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andyalderCommented:
Personally I'd set up one big RAID 10 and slice it in two, but it depends on what SAN it is. You're no doubt aware of the RAID 5 write penalty which requires 4 physical I/Os per logical I/O (although cache improves this a bit).

It's a toss-up though, if SQL is really busy Exchange will slow down but on th other hand if SQL isn't very busy Exchange will benefit from the extra I/Os of having more disks available.
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PaperTigerAuthor Commented:
It's an EMC AX4 iSCSI. I can expand to 12 drives later, but currently have 6.

Why would you say it's a toss-up? I would imagine having one system affecting another is not a good idea.
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andyalderCommented:
Having twice the I/Os available is a good idea though, that's why it's a toss up. Maybe Exchange and SQL are creating exactly the same amount of I/O as each other, then it wouldn't matter which way you do it. But what if Exchange needs twice the I/O as SQL, you'd have to re-provision the disks to tune performance if it was two seperate arrays, it would do it automatically if both LUNs were on a single set of spindles.
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PaperTigerAuthor Commented:
Would you please clarify the last sentence "it would do it automatically if both LUNs were on a single set of spindles?"

I really appreciate your insight here.
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andyalderCommented:
I simply mean that if you have 1200 IOPS available in the spindle set and SQL is only taking 400 then there are 800 available for Exchange. If it was split into two with 600 IOPS on each set of disks you couldn't gain the extra 200 IOPS. Of course it's swings an roundabouts, heavy SQL action will slow Exchange down. Pity you haven't got the CX4 since you can define quality of service with that, but of course you pay more for that functionality.
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PaperTigerAuthor Commented:
Thank you so much, Andy, I'll take your advice to go RAID 10!
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