1. A method for a host computer to recover unused storage space in a thin-provisioned volume presented by a storage server, the host computer mapping a file to logical blocks in the thin-provisioned volume, the storage server mapping the logical blocks to storage space in the storage server, the method comprising: (1) the host computer deleting the file from the host computer by unlinking the file from the logical blocks but without returning the logical blocks to a pool of free logical blocks to be mapped to files by the host computer; (2) in response to (1), the host computer issuing at least one SCSI write-same command to the thin-provisioned volume, the at least one SCSI write-same command comprising a data block of all zeroes addressed to at least some of the logical blocks, the at least one SCSI write-same command causing the storage server to (a) map the at least some of the logical blocks to a common storage space of all zeroes shared by any logical block with all zeroes and (b) free at least some of the storage space previously mapped to the logical blocks; and (3) in response to (2), the host computer returning the logical blocks to the pool of free logical blocks.