I heard you can expand a raidz if you add one with the exact same setting. So is it true that I can build a raid-2z now using 4 disks (so I have 2+2) and later on add another 4 disks so I have a raid-2z with 6+2? Or will this lead to 4+4? Is it even possible to have 3+1 now and add 4 drives so I have 6+2?

I ask this because I want to have 6+2 in the future but do not have enough money to buy all drives by now.