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From: steve@drivax.UUCP (Steve Williams)
Newsgroups: net.eunice,net.unix-wizards
Subject: Re: Question about mag tapes under Eunice
Message-ID: <62@drivax.UUCP>
Date: Fri, 7-Dec-84 02:01:48 EST
Article-I.D.: drivax.62
Posted: Fri Dec  7 02:01:48 1984
Date-Received: Mon, 10-Dec-84 01:44:12 EST
References: <162@prcrs.UUCP>
Distribution: na
Organization: Digital Research, Monterey, CA
Lines: 35
Xref: watmath net.eunice:188 net.unix-wizards:10870

> 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