1. A data storage apparatus comprising: a storage medium; a flash memory buffer configured to store write data to be written in the storage medium; and a controller configured to regulate a data transfer operation between the flash memory buffer and the storage medium, wherein the controller compares the amount of unused space in the flash memory buffer to a first reference value and compares the amount of valid data in the flash memory buffer to a second reference value, and in response to the comparisons, conducts either a block reclaim operation on the flash memory buffer or a buffer flash operation to transfer valid data from the flash memory buffer to the storage medium.