Did you try
Edgar Fuß <ef%math.uni-bonn.de@localhost> writes:
> I have a DDS tape (written on an IRIX machine) with 2M blocks.
> Any way to read this on a NetBSD machine?
> My memories of SCSI ILI handling on DDS are fuzzy. I remember you can operate
> these tapes in fixed or variable block size mode, where some values in the CDB
> either mean blocks or bytes. I thought in variable mode, you could read block
> sizes other than the (virtual) physical block size of the tape.
dd if=/dev/rsd0d of=FILE bs=2m
or similar? I believe that dd does reads of the given bs and these
reads are passed to the tape device driver which then does reads of that
size from the hardware, and that this then works fine.