It's really more of a cluster question than an exchange question.
1. Cluster only supports basic disks.
2. Cluster keeps track of the signature for each disk resource.
Given 1 and 2 above, I would:
1. Create a new RAID set.
2. Create a new disk resource from the new RAID set.
3. Add the new disk resource to the MSExchangeSA dependencies.
4. Use ESM to move the database to the new disk.
5. If necessary, move the tracking logs and gatherer logs.
6. Remove the old disk from the MSExchangeSA dependencies.
7. Take the old disk off line.
8. Remove the old disk's disk resource.
9. Remove the old disks.
If you want to use the old members as part of the new disk, it gets quite a bit more complicated. Basically, you record the drive letter and signature of the old disk, back up the data, destroy the old set, create the new set, swap the signatures and drive letters, and restore the data. You'll probably want to bring in a consultant if you decide to go this route.
John
MOSMWNMTK