The VM portion of Netbackup is capable of having a centralized database.
However the BP portion of  netbackup requires each media keeps a small
database that maps image ID to tape name and other associate information
like the where this image is located on the tape.

It's important to think Netbackup having two semi-independent components.
VM controls robot, volume databases and knowing physically where the
tapes are in the robot (or not).  The BP portion controls backup,
scheduling, and knowing where a backup image sits on which tape.

Why there's a tape assigment concept in the BP portion of the code?  I'm 
not defending Veritas (they bought it from Backup Plus).  However being a
programmer in my previous life, I can imagine the tape assignment (to a
media server) is a way to simplify system design.  This is a way to ensure
once a particular backup or restore job starts, the media server is able 
maintain a single TCP connection (for the data) to the client even when it's 
necessary to span multiple tapes.  Having client to maintain a single TCP 
connection for the whole data transfer of a single backup image is important.  
This will help make the client software stateless.  If during the tape
spanning, the backup/restore datastream can be switched from one media server 
to another, the client software will be quite a lot more complicated.

I'm not saying the same thing can't be achieved without the tape assignment
concept.  However tape assignment simplifies the programming.

--Mike


> From veritas-bu-admin AT mailman.eng.auburn DOT edu  Thu Mar 16 10:58:52 2000
> 
> 
> 
> Why is the behavior extremely useful/necessary? If we have a centralized 
> catalog of media, and we don't duplicate media id's or barcodes, why can't 
> the 
> individual media servers update a certral database, rather than keeping their 
> own?  Why do I need to run a bunch of commands to migrate tapes from one 
> robot 
> to another?  Maybe I want to *easily* migrate tapes out of one robot and into 
> another in another location, have the robot simply re-inventory itself, or 
> use 
> vmadm/other commands to import tape into a robot.
> 
> Why is it so difficult, and what is the design philosophy behind it?
> 
> Thanks.
> 
> -- 
> Andy Steingruebl              | e-mail: steingra AT pprd.abbott DOT com       
>    
> Unix Systems Admin/Programmer | phone:  (847) 935-4728                    
> Unix/Network Security         | fax:    (847) 935-0142                    
> Abbott Laboratories, PPDR&D   | post:   100 Abbott Park Road, D472 - AP9A
>                               |         Abbott Park, IL 60064-6115
> 
> 
> 
> _______________________________________________
> Veritas-bu maillist  -  Veritas-bu AT mailman.eng.auburn DOT edu
> http://mailman.eng.auburn.edu/mailman/listinfo/veritas-bu
> 


-- 
Mike Wei       Collective Technologies, a Pencom Company
Email: wei AT colltech DOT com