I don't think that's correct for the case that dvdgsng is describing. IIRC, the RAIDZ vdev won't allow the use of any extra space until all of its drives have b

I don't think that's correct for the case that dvdgsng is describing. IIRC, the RAIDZ vdev won't allow the use of any extra space until all of its drives have been replaced with bigger ones. What you're describing occurs when growing a ZFS pool by adding a new vdev, i.e. extra disks that sit alongside the existing ones. (Edit: Didn't realize that mbreese had already addressed this point in a different reply.)