On ZFS, a pool is resized by replacing all the drives in the pool. When autoexpand=on and the last drive is replaced, the pool will have expanded capacity. And drives are cheap.
When another RAID device is added to the pool instead, it is used as a stripe. Different types of RAID can be combined in this way, for example one can add a mirrored stripe to an already existing RAID-Z. Whether this is desired or not is a different discussion, since the point here is that both scenarios are possible.
Unlike other volume managers, ZFS expands on the disk boundary, rather than physical or logical elements; it's a larger boundary, but since no arcane or complex procedures or knowledge are required and drives are cheap, it's very practical, as well as elegant.
When another RAID device is added to the pool instead, it is used as a stripe. Different types of RAID can be combined in this way, for example one can add a mirrored stripe to an already existing RAID-Z. Whether this is desired or not is a different discussion, since the point here is that both scenarios are possible.
Unlike other volume managers, ZFS expands on the disk boundary, rather than physical or logical elements; it's a larger boundary, but since no arcane or complex procedures or knowledge are required and drives are cheap, it's very practical, as well as elegant.