Lets say I have 3 2TB disks in a RAIDZ configuration. How much space do I really have to use and how easy is it for me to add another 2TB drive to the array? Do I gain a full 2TB of free space?
If you want to add extra drive in RAIDZ you'll have to recrete the array with extra disk. Which mean you have to back up all of your data. The capacity for RAIDZ is still N-1. For RAIDZ2 its N-2