When a volume belonging to a first storage tier is relocated to a second storage tier, in the event that an empty volume satisfying capacity conditions is not present in the second storage tier, an empty volume satisfying the capacity conditions within volumes belonging to a third storage tier is virtually...http://www.google.de/patents/US7434017?utm_source=gb-gplus-sharePatent US7434017 - Storage system with virtual allocation and virtual relocation of volumes
