I would not multiplex to a value like "25" if only for the reason that
the higher the MPX value, the greater the number of tapes over which
your backup image will be distributed, and therefore, the greater the
chance that a single media failure will affect a given restore...

For example. 
1 client with 100 Gig of data on 1 tape.
That one specific tape, if it fails, will affect 1 restore, or say 2
restores if there is a second 100Gig image on a 200Gig tape.

25 clients with 100 Gig each, of Data, MPX=25.
Over 200 Gig tapes, you would use ~12 tapes.
If 1 of the 12 tapes is trashed, you now have 25 images you cannot
restore.
Also, if you get a media write error on that 1 tape/drive during a
backup, you have 25 failed backups.

Assuming your 25 clients are 100Mb/s network clients, each one can
probably push about 8MB/s of data....in a well tuned machine, you might
be able to pull 8 of these clients in a single GigE NIC card on your
media server, so you have to have 3 GigE cards to pull these 25 clients
into your media server....which is more raw data than most current tape
drives can write....ignoring the fact that the media server's PCI
bus&bridge are working so hard to pull data via 3 GigE cards, that it's
unlikely to have enough bandwidth to properly drive the data via the HBA
to the tape drive.

Paul




-- 


> -----Original Message-----
> From: veritas-bu-bounces at mailman.eng.auburn.edu 
> [mailto:veritas-bu-bounces at mailman.eng.auburn.edu] On Behalf 
> Of WEAVER, Simon
> Sent: July 31, 2006 1:45 AM
> To: 'Liddle, Stuart'; 'Mansell, Richard'; 
> veritas-bu at mailman.eng.auburn.edu
> Subject: Re: [Veritas-bu] Multiplexing
> 
> 
> 
> Stuart
> Completely disagree - we get the best of both worlds and 
> restores have never
> been any real issue for us, even large amounts of data across multiple
> tapes.
> 
> Regards
> 
> Simon Weaver
> 3rd Line Technical Support
> Windows Domain Administrator 
> 
> EADS Astrium Limited, B23AA IM (DCS)
> Anchorage Road, Portsmouth, PO3 5PU
> 
> Email: Simon.Weaver at Astrium-eads.net
> 
> 
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