> Could you force a complete rewrite if you wanted to?
On btrfs that's a rebalance, and part of how one expands an array (btrfs add + btrs balance)
(Not sure if ZFS has a similar operation, but from my understanding resilvering would not be it)
Not that it matters much though as RAID5 and RAID6 aren't dependable upon, and the array failure modes are weird in practice, so in context of expanding storage it really only matters for RAID0 and RAID10.