Question about mag tapes under Eunice
Steve Williams
steve at drivax.UUCP
Fri Dec 7 17:01:48 AEST 1984
> Maybe someone can enlighten me as to why this works the way it does:
>
> My wife works on a Eunice system (version 3.2). I gave her a mag
> tape with some stuff written on it in tar format (V7 tar, 1600 bpi).
> She was able to extract it using tar on her Eunice machine with no
> problems. She then put some things on the tape to give me, again,
> using tar. She had no problem putting things ON the tape, but when
> she tried to get a table of contents listing, tar complained about
> the block size being zero and no TOC was generated. She recreated the
> tape with tar, only this time put a blocking factor (tar cvb 20 files).
> Again, there was no error, but when she tried a TOC, the same error
> happened. At this point, she gave up and gave the tape back to me.
> I mounted the tape on my machine and managed to generate the TOC AND
> extract the tape with no problems (and yes, the files were the files
> that SHE put on the tape, not the ones I put on). I don't understand..
>
> Why is that VMS/Eunice can't read its own writing?
The default block size on a tape mounted with the VMS /FOREIGN switch is 512.
To read a blocked tar tape, you need to set the block size to a value greater
or equal to the block size on the tape. For tar b 20, the block size is
20 x 512 or 10240. Magic incantations which are known to work::
$ mount mtxx:/for/block=65534
(te16)
$ mount mfxx:/for/block=65534
(tu7x)
65534 is the maximum value for the /block parameter. This allows you to read
the tape even if you don't know the blocksize.
-Steve Williams
{ihnp4,mot,ucscc,amdahl}!drivax!steve
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