Your description is far more elaborate than mine. Thanks.
-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Musselman, Paul
Sent: Friday, May 14, 2010 6:17 PM
To: Midrange Systems Technical Discussion
Subject: RE: Ultrium 4 Tape Initialization
Dan Kimmel wrote:
INZTAP CLEAR(*NO) does leave files on the tape but they're in deleted
status. Next time you write to the tape they'll be overwritten.
Dan--
Well, sort of-- the files aren't really deleted-- they're not actually
touched at all! But they will be overwritten.
Tape is a serial medium-- just like a VHS tape. Disk is more like a
DVD. With a DVD you can select the scene you want to see and >bingo<
you're watching it. With a VHS tape you have to fast-forward or rewind
until you get to the spot you want.
All the system does when a tape is initialized with CLEAR(*NO) is rewind
to the very beginning of the tape and write a new tape label (ie the
tape name or number) and a pair of Tape Marks, which indicate
End-Of-Tape. Any data on the tape after the two tape marks is not
touched.
One of the rules of tape is that you can't update part of a file written
on that tape, so you couldn't mark a tape file as 'deleted.' If you
have 100 files on the tape you can tell the system to position the tape
to sequence number 76 and replace 76 with new data-- but this
effectively 'wipes out' the original files 76-100. When the new #76 is
completely written (starting at the same place on the tape where the
original #76 started) the system adds end-of-tape 'headers' and two tape
marks, indicating that the tape now ends after the new file #76. The
remains of the original files 76-100 are still there-- the parts that
didn't get written over by the -new- file #76.
Paul E Musselman
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