BTW, just as a frame of reference, the last time I used an Essbase server with local storage was back in 2008. It had a mirrored pair for the OS (raid 1), and 10 disks for Essbase configured as raid10 (12 disks total). The Dell guy who built it for us considered:
-- optimal stripe size based on Essbase block size
-- using two raid controller channels to split up the work at a physical level
-- multiple os luns to allow the OS to optimize reads/writes
-- raid alignment (which I was told is critical)
Calcs were more than twice as fast than the former server which had similar RAM and processors, but a 5 disk RAID5 set.