Tracy's description of RoadRunner's behavior does not match my experience
with the product.  In fact it is quite rare for multiple volumes to fill up
at the same time.  We used RoadRunner for a number of years in an
environment with two tape drives.  Three-tape backups were quite common.

I believe the way it works is that RoadRunner/Backpack determines at the
outset which files will go to which drives.  If all the files destined for
one drive can fit on one volume, it won't ask for another one on that drive,
even if the other drives require additional tapes.  In our case, we were
using the highest level of data compression, so the total amount of data
written to each device was difficult to predict, often resulting in uneven
distribution of the load among drives.  In a situation where the volume is
more predictable, I suppose the behavior Tracy describes is more likely.

-----Original Message-----
From: Johnson, Tracy [mailto:[log in to unmask]]
Sent: Monday, May 06, 2002 11:05 AM
To: [log in to unmask]
Subject: Re: Thinking about a new tape drive


The only drawback to performing the Parallel method, is that you must
monitor of how much tape is used over time.

This is because when it goes *over-the-edge* (at least in
BackPack/RoadRunner) so it needs to write to more than the number of tapes
specified, you're required to double the number of tapes used.

i.e,

If you write parallel to 2 tapes and the job wants more, even if there is
only one more byte to go, you must insert 2 more tapes.

If you write parallel to 3 tapes and the job wants more, even if there is
only one more byte to go, you must insert 3 more tapes.

<snip>

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