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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