I recently spec'd two new Dell PowerEdge R710 servers for a small data warehouse. One for Analysis Services and the other for SQL Server. The choices for storage were constrained by capacity, performance and direct attach storage disk connections. I ended up choosing RAID 5 for both because I had to meet performance and storage requirements but was limited by 8 DAS connections. The AS system has an 8 x 146GB 15k rpm drive array and the SQL Server system has an 8 x 600GB 10k rpm drive array. Choosing a RAID 10 array could have been accomplished if I were willing to use slower disks to regain the capacity lost due to RAID 10 versus RAID 5. I'm convinced that RAID 10 is the right choice but can't escape practical realities.