> after installing OS a few times to get familiar with it and with zfs I > now want to install a "real" machine with 4 disks as RAIDZ2 rpool.
I don't remember where I read it, but I believe you can't do that. I believe you can only make the rpool on a mirror. What you could do instead: Suppose your disks are all 500G. Make a mirror from the first 2 disks. Assign only 100G (or whatever) to rpool. Create a new "datapool" with the remaining 400G Create a new mirror with the remaining 2 disks, and add it to datapool. Then your datapool is 900G, and I think that's the best you can do with those 4 disks.
