I gave the proper explanation for RAID 1 and RAID 5. I over-answered and included the differences for RAID 0, 6, 10 including a discussion of the pros/cons of 6 vs 5 these days. I use to know even the esoteric ones like 2-4 and some of the odder combinations for specific uses. This one is a gimmie considering the recruiter asked about it too so any applicant could research it if they weren't familiar prior to interview.