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> Facebook runs their entire stack using Btrfs

Yeah, and when I was there machines would run out of disk space at 50% usage and it took months to figure out why. In the mean time, they'd just reimage the machine and hope. I don't recall any issues with data loss, but it didn't have the air of reliability.

But my team was weird at FB, our uptimes of 45 days were way above the average, and we ran into all sorts of things because we operated outside the norm.