I am trying to transfer information from an SCO Open Server 3.0
          system to an SCO OpenServer 5.0 system using magnetic tape.  I
          make the backup using tar or cpio on the source system, but I
          cannot read the tape on the destination system.  I have the same
          problem when I try to transfer information from an SCO OpenServer
          5.0 system to an SCO Open Server 3.0 system.

          DAT tapes using the DDS II format seem to be very sensitive to the
          blocksize being used by the SCSI driver. If the blocksize is
          different on the target system than that being used on the source
          system, the tape cannot be read.

          Set the SCSI driver blocksize to be the same on both target and
          source systems.  This can be done with the setblk option to the
          tape(C) command.  The blocksize can be set to variable mode using
          the command:

             # tape -a 0 setblk

          This has not worked in all cases.  A better option is to set the
          blocksize to a specific value.  For example, set the blocksize
          to 1024 bytes with:

             # tape -a 1024 setblk

          This command should be issued on the source system before making
          the backup, and on the target system before attempting to restore.

          The tape command is not supplied as standard with the Open Server
          Release 3.0 operating system.  It is contained within Support
          Level Supplement (SLS) UOD376C, which is available for downloading
          from the SLS directory at ftp.sco.com.

          Technical Article 104421, "UOD376C Enhanced SCSI Tape Drivers support variable
          block tape drives".