reading AND writing an exabyte tape

[Jeremy Higdon]

In article <1991Mar7.005651.16891 at ccu1.aukuni.ac.nz>, russell at ccu1.aukuni.ac.nz (Russell J Fulton;ccc032u) writes:
> I have been trying to implement a system to enforce tape label checking for
> our backup system. 
> If I first verify that the operators have mounted the right
> tape by reading the label which has been previously written on the tape and
> then try to write to the tape I get an I/O Error.
> 
> If however I rewind the tape after reading the label and then fsf the tape
> all works as expected. 
> 
> i.e. It would appear that one must rewind the tape when switching between
> reading and writing. Is this behavior intentional? On other systems I have
> had programs that read their way down to the end of a tape and then appended
> data. 
> 
> Is this the reason why -a option of tar does not work?
> 
> Thanks, Russell.
>  
> -- 
> Russell Fulton, Computer Center, University of Auckland, New Zealand.
> <rj_fulton at aukuni.ac.nz>

The Exabyte does not allow write after read.  It allows writes only from
BOT, bottom of filemark, or blank tape.  Your fsf must happen to position
you at blank tape.  So the behavior that you're seeing is correct.