I'll add this: on spinning disks it's normal to reorder write operations; it is optimal to order writes in a way that matches the layout on disk. That way, eac

I'll add this: on spinning disks it's normal to reorder write operations; it is optimal to order writes in a way that matches the layout on disk. That way, each sector is written as the write head passes over the sector. We like to think of a disk-backed filesystem as slow, persistent RAM, but in reality it's a lot more complex than that.