Affinity and anti-affinity scheduler filter

Our consumers who build their application on top of volumes would like to be able to set affinity or anti-affinity between new volumes being created and existing volumes. One use case is DB team build MySQL master onto one volume, they'd prefer to put new volumes for slave DBs to different backends from where the master DB resides, for the sake of high availability. Another use case is a log processing project would like to have fast storage as possible, so they create soft RAID across multiple volumes。 They want to put these volumes as close to each other as possible, ideally on the same storage backend.