Aspects of the present disclosure are directed toward a computer program product for managing the migration of extents on tiered systems. The computer program product can be configured to receive a space reservation request for one or more requested extents on a first storage tier of a storage system. The computer program product can also be configured to release 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 computer program product can also be configured to migrate the one or more requested extents to the first storage tier reserve space.