Thanks, I appreciate the info.
I think I will put 2 x 1 tb in a cache array , the 2 x 4TBs mirrored and put data there (mirrored seems safest for data integrity and probably the same with the other 2 x 1 tbs).
So 1 zfs Cache array with 2 x 1tb, 1 mirrored data array with 2 x 4 tb, and 1 mirrored data array with 2 x 1 tb.
In the end I am giving up a 1/2 my drives for data safety I guess.
1 more question, if I am running all SSDs (as the N1 is built for) why do I need cache, everything is running at the speed of SSD?