Earlier quoted context omitted.
> It is possible with windows storage space (remove drive from a pool) and mdadm/lvm (remove disk from a RAID array, remove volume from lvm), which to me are the two major alternatives. Don't know about unraid. Perhaps I am misunderstanding you, but you can offline and remove drives from a ZFS pool. Do you mean WSS and mdadm/lvm will allow an automatic live rebalance and then reconfigure the drive topology?
So for instance I have a ZFS pool with 3 HDD data vdevs, and 2 SSD special vdevs. I want to convert the two SSD vdevs into a single one (or possibly remove one of them). From what I read the only way to do that is to destroy the entire pool and recreate it (it's in a server in a datacentre, don't want to reupload that much data). In windows, you can set a disk for removal, and as long as the other disks have enough s…
This kinda implies that you can't actually remove data vdevs, because in practice you can't rewrite all references. You also can't do offline deduplication without rewriting references (i.e. actually touching the files in the filesystem). And that's why ZFS can't deduplicate snapshots after the fact.
On the other hand, reshaping a vdev is possible, because that "just" requires shuffling the vblock -> physical block associations inside the vdev.