Short: Scsi-Direct Tape Handler by Mathew Dillon

FEATURES: My tape-handler implements fully asynchronous double-buffered read and
          write operations.  If you have disk/tape drives which support
          reselection then the handler will be able to operate on the tape
          concurrently with disk accesses meaning that an archiver such as
          Tar will not 'freeze' while tape operations are in progress.
 
          To take the greatest advantage of this feature you should specify as
          large a buffer as possible.  Anywhere from 500K to 2MB will yield
          reasonable throughput.