> Preston de Guise 
> 
> NetWorker rewinds the tape to make sure that it's writing to the 
> correct tape; I also believe part of the other purpose is that when 
> it's finished writing it will write a double-EOF to signify current 
> end of tape. When it's time to start writing again, it goes back and 
> writes over the _second_ end of tape so that there's just a plain EOF 
> marker between the two savesets. That behaviour was explained to me 
> over a decade ago though so apply standard caveats to it :-)

That might explain some tape errors we've seen over the entire time we've 
been running (Sun's OEM-ed) 7.2. I know... it should be replaced by 7.5.x 
in a few weeks hopefully! We started seeing them immediately after 
upgrading from 6.1 to 7.2, on the same hardware, same OS, two different 
servers, etc., etc.

Networker would write just fine to a tape and then with a completely 
random frequency fail to write a subsequent backup to the same tape at 
some later point. It would load the tape, seek forward, keep on seeking 
until it reached end of media, rewind and try a few more times. Usually, 
it would then eject the tape, get another and backup successfully. Usually 
(!) the delays introduced by such issues didn't cause problems.

My empirical theory (supported in concept by Sun and neither denied nor 
ever fixed by EMC) was that some kind of final "end of data" marker was 
not being written properly in some instances. This might explain the 
/complete/ randomness of the errors: new tapes, old tapes, one pool, 
another pool, ad infinitum, if that second EOF wasn't being reliably 
written to tape. It also makes me feel better that any previous backups 
written to said tapes are probably OK and shouldn't present issues if 
being read for clones, etc.

Hmmm...  :-)

Oh well - Hopefully this is not an issue anymore.



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