Right, the free space buckets are a fine analogy. They are conceptually similar in some ways to the free space in the hot standby drive. I don't think from a d

Right, the free space buckets are a fine analogy. They are conceptually similar in some ways to the free space in the hot standby drive. I don't think from a data safety or performance perspective pre dRAID vdev really differ too terribly much from raid 50 setups. (They do differ greatly in administrative flexibility, versus the insanely rigid approachs of traditional hardware raid). But yeah, after replacing the failed drive, ideally dRAID would basically do just what it did after drive failure in reverse. (End result: No longer having any drives holding data for a different vdev than they belong to). Obviously this means writing basically that whole disk, and reading from potentially every disk. But as you mention you are spreading the load out across the whole array, hopefully reducing the overall impact, and being less likely to stress any drive into dying.