Couchbase server upgrade from 1.8 to 3.0 directly

Couchbase Server
4

Hey Matthew!
I have to upgrade first whole cluster from 1.8.1 to 2.2 and then 2.2 to 3.0.1, or just each node upgrade from 1.8.1 to 2.2 and then 2.2.to 3.0.1.?

Thanks in Advance.