One problem with mirror vdevs vs. RAIDZ2 : In the RAIDZ2 case you can lose any two drives and still have your data, in the mirror vdev case, 2 drives failing in

One problem with mirror vdevs vs. RAIDZ2 : In the RAIDZ2 case you can lose any two drives and still have your data, in the mirror vdev case, 2 drives failing in the same vdev means all your data is gone. You could potentially be okay with losing half your drives, but only if all the failed drives happen to be part of different vdevs.