It appears as though you are asking whether you can have two instances of the same RAC (in an active-passive configuration) connected to different set of disks.
The answer to this question is no. To quote from the Introduction to Oracle RAC linked to in the comments of your other question:
An Oracle RAC database is a shared everything database. All data
files, control files, SPFILEs, and redo log files in Oracle RAC
environments must reside on cluster-aware shared disks, so that all of
the cluster database instances can access these storage components.
This means that each node in a RAC must share the same disks, whether both are active or not. You could, I guess, rebuild the cluster between tests to have a different disk-layout but I don't see the point as you state in the comments that you have two clusters, i.e. at least 4 nodes.
Obviously, if you only have a limited set of disks you're going to have to rebuild anyway but if you want to do a proper comparison and you have two identical RACs set one up as a RAID-10 and the other as a RAID-5 and start testing.
Would it be feasible (for testing) to just use a single instance (ie.
NO RAC) and run tests using RAID 5 layout and then change the layout
to RAID 10 and re run the tests? What advantages/extra information
does using RAC clusters when testing have?
As stated above I don't see the point. However, it depends on how you are going to use the RAC and what your intention was in getting two. There are 2 main reasons for using a RAC:
- The ability to have multiple servers accessing the same database.
- To enable fast recovery from a failure.
Whether you want to test with a single active node depends on your reason for obtaining this architecture. If you intend to run your RAC as an active-passive, i.e. one node is active and the RAC fails over to the passive node in the event of a failure in the active then by all means run your tests on a single instance (and ensure that you test whether it fails-over correctly)
If you intend to run the cluster as an active-active then it makes little sense to run tests on a single active node as this is not the configuration you intend to have.
To clarify based on your comment. You have two RACs. That means you have 4 servers, two sets of disks and two databases.
A simple diagram might look as follows:
Server 1 \
--- RAC 1 --- Set of Disks 1 - Database 1
Server 2 /
Server 3 \
--- RAC 2 --- Set of Disks 2 - Database 2
Server 4 /
The two RACS are in no way related so of course you can use two different RAID set-ups on them.
You can set them all up to use the same database but that isn't what you want to do.