On Fri, Sep 01, 2006 at 08:56:15AM +0200, David Sánchez Martín wrote:
> 
> Now for something completely different ( ;-) )
> 
> The chg-zd-mtx changer script knows about barcodes, but,
> What's the difference between using it or don't?
> Just time looking for the next tape on the changer?,
> or it will refuse/warn to load a non/bad barcoded tape?
> 

Keep in mind, this answer is from someone who never used a
tape barcode system ...

Last query first, I don't know if chg-zd-mtx will refuse to
even consider a non-barcoded tape if it is told the library
has a reader.  Even barcoded tapes have to be labeled with
amlabel.  Other parts of amanda certainly refuse to use a
tape with an inappropriate amanda tape label.  But that is
an entirely different issue than I think you are asking.

Using barcodes has advantage, it seems to me, only if you
move through your slots in a non-sequential manner.  During
restores, or if the library has multiple drives used for
multiple configs and tapes are loaded from different parts
of the library would be two such examples.  Or maybe you are
weird and load your slots with tapes in an arbitrary order.
For most of us the tape in slot 5 is used after the tape in
slot 4.  So going the slot 5 "directly" because of a barcode
database, or sequentially because it is the next slot is the
same.

When the movements are not to sequential slots, there are
additional advantages to direct moves besides time saved.
Without a barcode db, amanda must load, rewind, read, and
unload each intervening tape causing additional wear on
the tape and the robotics.

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
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