Portability is not really an aspect one needs to consider when it comes to a NAS. Performance hits? Z1 will have performance issues when running in a simple mirror (especially for writes), but with 4+ disks that reduces significantly.
Sure scrubs will take longer on a multi-disk array, but again for a home NAS, the goal is maximising data storage capacity without a major hit on performance, ideally being able to saturate the most common gigabit LAN connection and have some more bandwidth available for local processing.



KSP2 comes to mind