A storage system according to one embodiment includes logic adapted for determining to move an extent from a source-tier in a storage system to a destination-tier in the storage system, wherein a set of tracks of the extent is presently being accessed; logic adapted for determining whether any track from the set of tracks is presently being written to; logic adapted for designating to a write-stack associated with the source-tier each track that is presently being written to and designating to a read-stack associated with the source-tier remaining tracks from the set of tracks; logic adapted for removing oldest tracks from the read-stack and the write-stack until the read-stack and the write-stack have been depleted of tracks; logic adapted for populating a destination-tier cache with the tracks as they are removed from the read-stack and the write-stack using a predetermined read-to-write ratio when a parameter of the extent exceeds a migration threshold; logic adapted for removing any tracks from a source-tier cache that were removed from the read-stack and the write-stack; and logic adapted for migrating the extent from the source-tier to the destination-tier.