Jon, 

Very good point here. Typically I have tried to tune systems and settings to
where the tape drive is not having to reposition and have based my comments
on this. Out of the box, NBU does not do a great job of keeping a drive busy
100% of the time and tuning is required to achieve this. 

Thanks for pointing this out. 

dave

-----Original Message-----
From: Jon Walton [mailto:jonw AT n2h2 DOT com] 
Sent: Monday, May 20, 2002 6:49 AM
To: Dave High
Cc: WEAVER, Simon; 'veritas-bu AT mailman.eng.auburn DOT edu'
Subject: RE: [Veritas-bu] Multiplexing

Multiplexing can help you write more to a tape if your non-multiplexed
stream is not loading the tape drive to its maximum throughput.  On
average I get 80G on a DLT8000 (multiplexed) vs 60G
(non-multiplexed).   It is my understanding that anytime the tape drive
has to back-hitch, you will lose some actual tape capacity.

-Jon

On Mon, 20 May 2002, Dave High wrote:

> Simon, 
> 
> Multiplexing will not help you write "more" info to a tape. A tape can
hold
> a specific amount of data based on tape format and compression. Once it is
> full, it is full. Using Multiplexing can help you use less tapes during a
> backup run since more streams are filling up a single tape rather than
> loading three tapes and writing to them, but NetBackup will continue
loading
> and using a tape until it is full, then it will move on to a new tape. 
> 
> Also, on other thing I wanted to point out about the bpexpdate command is
> that it does NOT "erase" a tape it simply removes the NetBackup Catalog
> reference to that tape and allows it to be overwritten. The data is still
on
> the tape until it is overwritten. The only reason I bring this up is for
> security reasons. If you need to get rid of the data on the tape, you need
> to bpexpdate it, then run a big magnet over it to wipe the data. 
> 
> Hope this all helps. 
> 
> dave
> 
> -----Original Message-----
> From: WEAVER, Simon [mailto:Simon.WEAVER AT astrium-space DOT com] 
> Sent: Monday, May 20, 2002 5:45 AM
> To: 'veritas-bu AT mailman.eng.auburn DOT edu'
> Subject: [Veritas-bu] Multiplexing
> 
> Firstly, Thank you all for your help with BPEXPDATE. I am glad I am
getting
> this right now :)
> 
> I have one small question about Multiplexing. On the Netbackup PDF's
(which
> is what I am using) it says you can specify the number of jobs that can
> multiplex to a single tape drive! (Words to that effect).
> 
> My question is this: I have a backup policy with 8 clients listed. Within
> this backup policy I have specified to backup All Local Drives for these 8
> clients. I want to use as less tapes as possible (I use 100GB HCART
Tapes).
> If I increase this Multiplexing number, does it mean that more data will
be
> written to a single drive in a tape?
> 
> We use an ADIC Scalar 100 which consists of 3 tape drives. Because I have
no
> more slots available to place blank tapes, I was kind of hoping that using
> this Multiplexing option will help retain more data on a single tape!
> 
> Am I right, or am I reading this incorrectly.!
> 
> Thank you
> 
> Simon Weaver
> NT Domain Administrator
> Ext. 5544
> Tel: 02392-705544 (Direct Dial)
> Simon.Weaver AT Astrium-Space DOT com
> 
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