On the cost issue
I agree 100% that RAID 10 will always cost more than RAID 6, with the one exception being a 4 disk array. After that 50% overhead point, RAID 6's capacity overhead begins to go down while RAID 10 stays at 50%.
I mentioned in the article that this would be the case.
As far as cost is concerned, if the end result is more performance-driven than capacity driven, RAID 10 should be given serious consideration, even if it means some extra dollars up front.
That said, in many cases - especially for smaller shops - capacity is the key driver and as long as RAID 6 can keep up performance-wise, it will win the capacity argument every time.
I am careful not to take too hard a stance in these postings. While, in my opinion and experience, RAID 10 has been a good solution, there are certainly instances in which RAID 6 is an excellent solution. Based on the application at hand and the budget, these will be individual decisions.
