[ceph-users] crush rule question

Hi , i have a question regarding crush rules. I try to have the following: i have domain faillure on rack. currently we have 2 racks what i want to make is a crush rules for 3 replicas where at least 2 replicas are put on 2 differents rack and the third one can be on any of the 2. Is this possible and if yes how to write the crrush rule. Kr Philippe Van Hecke.