> The feature@raidz_expansion on-disk feature flag must be enabled to initiate an expansion, and it remains active for the life of the pool. In other words, pools with expanded RAIDZ vdevs can not be imported by older releases of the ZFS software.
Interesting - this indicates that the resulting vdev is on-disk different than a fresh vdev would be. Normally when you have a RAID expansion/level change, the format during the conversion is different, but when it is complete the on-disk is identical to it having always been that way.
