Uncertainty when changing to RAID 1 or RAID 10 on IBM DS3512 storage system

Big packages full of new equipment are every IT guys dream. It just so happened a while back I received boxes and boxes of hard drives to expand some LUN's on my IBM DS3512.

There is a fun side to new equipment, unboxing it, installing it and seeing how much better it is than your previous gear. On the other side of the equation is the outright scary side, when you finally press that "expand" or "change raid level" button that activates an irreversible operation on your production equipment. No matter how much preparation and testing you do, there is always some anxiety associated with making big changes.

During the Christmas holidays I planned to upgrade an existing RAID 5 array to RAID 10, this will increase the IOPS through the roof. As always I read the documentation, ran through the scenario on paper and then on a test LUN. What I couldn't work out was what would happen when I finally pressed the confirm button to change the raid level from 5 to "1 or 10".

The IBM storage manager offers the option as follows:

Change > RAID Level > 1 or 10...

This caused me some concern, while all the other raid levels were a single option (0, 3, 5, 6), 1 and 10 were bundled together as a single option. A logical person would say RAID 1 is a mirror of 2 drives, so if your raid array has an even number of drives that is 4 or more, then RAID 10 will automatically be selected. Unfortunately I am not willing to take that risk, what about obscure propriety raid levels such as 1E that might support RAID 1 in a multiple drive configuration.

After searching the IBM redbook, the user manuals and the DS System Storage manual I was unable to find a solution. IBM also wouldn't provide me an answer, telling me the issue was a configuration issue and not a hardware issue. I am sorry IBM, but the technical capabilities of a product are not a configuration issue. I wasn't asking you to configure the product for me, just what the RAID levels of your product are capable of.



Don't worry, the DS3412 only supports RAID1 with 2 drives

Finally I was able to find the answer from the local services provider that I purchased the DS3512 from. The IBM DS3412 only supports RAID 1 with 2 drives, that means:

If { you select change raid level to 1 or 10  } AND
{ The number of drives in your array is 4 or more } AND
{ The number of drives in your array is even } THEN
  It will become a RAID 10
}

So a logical approach would have given me the correct answer, but anyone working in IT knows, relying on logic often results in failure.