Some examples described herein relate to reclamation of storage in a thin provisioned storage device. In an example, a determination may be made that storage space provisioned to a logical unit number (LUN) by a thin provisioned storage device is freed by a file system managing file system operations in the LUN. Storage space freed by the file system may be marked. Amount of marked storage space that may be released to the thin provisioned storage device may be determined, based on i) difference between rate of allocation and rate of release of storage blocks by the file system in the LUN, and ii) usage level of storage blocks in the thin provisioned storage device. The determined amount of marked storage space may be released to the thin provisioned storage device.