Yev here -> Good question! The ops team may have a different theory, but I think it's when they die! We still have 15k 4TB HGST drives in our fleet that are cru

Yev here -> Good question! The ops team may have a different theory, but I think it's when they die! We still have 15k 4TB HGST drives in our fleet that are crushing the game, and have been for years. That said, we'll eventually migrate off of them to get more density, but so long as we're not cramped for space, we tend to keep high-performing drives in our fleet for as long as we can. There is a math equation that flips after a certain point where we can get a lot more density by replacing those smaller-capacity drives - so that tends to be the other main driver for migrating the fleet. *Edit -> For giggles here's an OLD post where we dissect drive failure and talk about migration a bit -> https://www.backblaze.com/blog/3tb-hard-drive-failure/ https://www.backblaze.com/blog/3tb-hard-drive-failure/