For RaidZ cases, you need to rebalance all the strips, which is non-trivial to do online (you have to make sure if the power cut off during the rebalancing, you

For RaidZ cases, you need to rebalance all the strips, which is non-trivial to do online (you have to make sure if the power cut off during the rebalancing, you don't lose the data). Without rebalancing, I think it can end up with weird corner cases (for example, in RaidZ2 case, if you have the rest 5 disks full and added 1 more disk, you cannot write data into the pool because there is no place for parity. It is not a problem if the disks are balanced).