They finally added this to Oracle Solaris ('closed source' zfs) in 11.4 (http://blog.moellenkamp.org/archives/50-How-to-remove-a-top-level-vdev-from-a-ZFS-pool.

They finally added this to Oracle Solaris ('closed source' zfs) in 11.4 (http://blog.moellenkamp.org/archives/50-How-to-remove-a-top-level-vdev-from-a-ZFS-pool.html http://blog.moellenkamp.org/archives/50-How-to-remove-a-top-...) And there is work on it for OpenZFS: https://www.youtube.com/watch?v=Njt82e_3qVo https://www.youtube.com/watch?v=Njt82e_3qVo for zfsonlinux As far as I understand you can currently add and remove striped/mirror devices, but you cannot remove raid-z vdevs (ref: https://github.com/zfsonlinux/zfs/issues/9129 https://github.com/zfsonlinux/zfs/issues/9129) - so there is definitely work left to be done in this area. as an aside mdadm has surprisingly fantastic features in this area and can reshape pretty much any array type to any other. i was impressed by that.