1. A non-transitory computer-readable medium with instructions stored therein, the instructions, when executed by a processor, cause the processor to perform operations, the operations comprising: locking a first range of addresses corresponding to at least one data block of a logical volume on a composite data storage system; growing the range of locked addresses to a second range of addresses without an intermediate unlock, the second range of addresses encompassing a migration unit including the at least one data block; filling a data hole in the logical volume by allocating metadata associated with the logical volume for the data hole and mapping the data hole to a migration unit on a physical volume of the composite data storage system; and shrinking the range of locked addresses to the first range.