That strikes me as a bit contradictory, since I would consider RAID1 (plus the redundancy across enclosures) to be the equivalent to even "hotter"[1] spares. Un

That strikes me as a bit contradictory, since I would consider RAID1 (plus the redundancy across enclosures) to be the equivalent to even "hotter"[1] spares. Unlike the hot (warm) and cold spares for the RAID5/6, all the drives in the RAID1 are continuously in use, which means they're subject to wear-related failures [2]. If you're getting performance benefits from the RAID1, then the extra drives may not be wasted, but that's a separate topic. [1] Which I argue is a misnomer. To me, "warm spare" makes more sense, since it's powered up but not actively synced in any way. Some systems, configurably, even spin down such spares. [2] As I mentioned in https://news.ycombinator.com/item?id=17855632 https://news.ycombinator.com/item?id=17855632 some failures are power-on/spun-up related, which makes the availability of a truly cold spare even more beneficial.