> What can they buy for, say, US$1000, assuming that they have a > computer capable of handling anything? > > One 8 TB M.2 NVMe SSD - very fast. No fault-tolerance. Takes up to > 30 hours to be copied to other internal storage for backup. > > Three 4 TB SATA SSDs - moderately fast. Can be arranged in > triple mirror (RAID 1) for excellent fault-tolerance but only > 4TB of space, or performance can be traded off to get 8TB of > storage in RAID 5. This is significant. > > Five 2 TB SATA SSDs - can be faster than three. Choices include: > 2 x 2 stripe over mirror plus spare, for 4TB of space and > amazing fault tolerance; RAID6 for 6TB of space and very good > fault tolerance but less performance.
Of course, you can get those same 6GB without the performance worries of raid6 using 3x 4TB in raid 10. So overall the circumstances where raid 5/6 makes sense are a small minority. It's mostly for cases where total capacity is a lot more important than performance and even there, the benefit is only 33% in your scenario (8GB vs 6GB). And when total capacity is a lot more important than performance one would typically go for HDDs (where the performance impact of raid 5/6 tend to be even more pronounced). === Stefan
