Aspects of the present disclosure are directed toward a system for managing the migration of extents on tiered systems. The system can include receiving a space reservation request for one or more requested extents on a first storage tier of a storage system. The system can also include releasing a first storage tier reserve space that includes one or more first tier reserved extents in response to the first storage tier reserve space being insufficient for the reservation request. The system can also include migrating the one or more requested extents to the first storage tier reserve space.