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With just four drives, would you do: a) two RAID 1 arrays (OS + transaction logs, Data) b) 1 RAID 10 array partitioned, or c) 1 RAID 5 array partitioned?

Thanks!

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4 Answers 4

2 x RAID 1 , one for data and one for logs. You will get the best speed and redundancy from this combination.

EDIT: I originally anticipated you were excluding the OS. If you are going to put the OS on as well, I'd also consider 1 x OS disk, 1 x RAID 1 set for the data and logs, and the fourth drive for the tempdb. There's also the old favourite of 1 x OS and the other three in RAID 5, but performance is not as good.

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And OS on a separate drive, if possible. –  user3914 Nov 17 '09 at 19:55
    
Sorry with only 4 drives, do you mean 2 at RAID 1 or do you mean 1 at RAID 10? –  Rhett Nov 17 '09 at 19:56
    
I clarified in the edit. –  user3914 Nov 17 '09 at 19:59
    
So you'd sacrifice OS redundancy for tempdb? –  Rhett Nov 17 '09 at 20:04
    
no way would i use a single disk for anything. –  rorr Nov 17 '09 at 23:16

Short answer - it depends.

What are your requirements as far as disk IO, capacity, and redundancy? What's the ratio of reads vs writes, how fast is your data growing, are you doing lots of operations where tempdb is getting hit hard?

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Low transactions, 3 reads to 2 writes, no onsite support staff so any failure will require a consultant so uptime key. –  Rhett Nov 17 '09 at 20:29
    
that's actually pretty highly transactional for sql. –  rorr Nov 17 '09 at 23:15

I would go with option (a) because of the advantage you get when separating logs from data. Logs are written mostly sequentially, data is written mostly randomly. You don't really want your random writes interfering with your easy sequential writes.

For the RAID array that has the OS on it, you probably want to divide it into two partitions: one for the OS, one for logs. Although as one user commented in another thread, this issue borders on religious for some people.

There are numerous reasons to avoid using RAID 5 for databases, but I assume you are already aware of them. RAID 10 is much better, but you don't really have enough disks to use RAID 10 properly.

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I think this depends on the potential size of the databases compared to the size of the disks.

If you need a lot of disk space for your databases go with RAID 10 and a small OS partition. If you need even more space go RAID 5 with a small OS partition and take a performance hit on writes.

If you don't need the space then you're going to have to benchmark the two independent RAID 1 arrays V a single RAID 10 partitioned (interesting to know which one is better for your environment :) ).

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