Raid 10 on 10k SAS v Raid 1 on 15k SAS

[tgbaynes]

I have a decision to make for a fairly high IOPs database, which I am going to Virtualise.

At the moment the DB sits on our Dell SAN, using a 4 disk Raid 10 config, on 10K SAS drives.

This gives me more disk space than we need for the database, but a good level of redundancy.

I also have available, 3 15k SAS drives, which are larger in size. These could be configured in a RAID 1 array, with the 3rd disk marked as a hot spare.

My question is: would you see better performance in the RAID 10 on slower drives, or the RAID 1 on faster drives?

Thanks for your views!

[bateslabel]

I would say it depends on the database and the actual drives being used. If these are all newer drives then I think it would depend on the database. If its a database that is read from more than being written to, I would say the 15 k disks will probably perform a little better. Because you'll be reading from both disks on reads. If its a balanced equal reads and writes type database, or mostly writes, I would say the raid 10 with the 10 K drives would be better.

[mcowger]

Most vendor rate a 10K disk at about 150 IOPs, and a 15K disk at about 180 (some go a little higher, but the ratio is generally about the same).

As a result, ignoring cache effects, you'd expect a 4-disk RAID10 set of 10K drives to support around 300 IOPs on write and about 600 on read.

For the 15K drives, you'd expect around 180 IOPs on write, and about 360 on read.

The numbers speak for themselves, and thats ignoring extra positive effects of more queues.

When comparing 10K to 15K drives, If the # of drives of more than 50% more, go with the slower ones.  I'd definitly stick with your current design.