ZFS device removal is on its way but not quite in illumos yet. From Alex's blog post: "We’ll publish the code when we ship our next release, probably in March

ZFS device removal is on its way but not quite in illumos yet. From Alex's blog post: "We’ll publish the code when we ship our next release, probably in March [2015], [and we will] integrate into Illumos once we address all the future work issues."