CommVault is doing file-level dedupe.  Their point is that we already
have the file on tape, why back it up again.  What you're asking about
is sub-file-level dedupe, which would be silly to copy to tape in it's
deduped format, for all the reasons others have stated.

---
W. Curtis Preston
Backup Blog @ www.backupcentral.com
VP Data Protection, GlassHouse Technologies 
> -----Original Message-----
> From: veritas-bu-bounces AT mailman.eng.auburn DOT edu [mailto:veritas-bu-
> bounces AT mailman.eng.auburn DOT edu] On Behalf Of Jon Bousselot
> Sent: Saturday, April 26, 2008 7:30 PM
> To: VERITAS-BU AT mailman.eng.auburn DOT edu
> Subject: Re: [Veritas-bu] Deduping with Tape as a final destination
> 
> As I understand the PureDisk product, yes.  The copy that goes to tape
> will be the full data set.  I believe the product is positioned save
> space and time from the client and on the equivalent of a DSU.  You
can
> run PureDisk along with NBU, so the stream of data that comes from the
> client is inspected for duplicate data (on the media server), and then
> space is saved.  As a PD client, it inspects data at even smaller
> chunks, but does the work at the client and sends the changes to the
PD
> repository.
> 
> I looked at the Commvault 7 documentation, and it was not obvious to
me
> what the contents of the final tape copy would be.
> 
> If I were going to use tape as a final resting place, and use slow
cheap
> disk as a de-dup location, I would like the tape copy to be the
simplest
> format possible for reading in the future.  And it would be nice if
> those archive tapes did not need a complex road map of re-dup chunks
to
> assemble the data.  On a PureDisk server, you can eliminate duplicate
> data from all your client images, because at any time you can get that
> data back from the single instance which lives on your random access
media.
> 
> I'm having a hard time conceptualizing the process by which a 100G
> client de-duped down to a 20G backup tape would be processed for a
> restore.  The bits have to come from somewhere, which is why I'm a bit
> confused on how Commvault is doing it.  I need to read their docs
again.
> 
> -Jon
> 
> 
> 
> > So, ultimately, the data copied to the tape will be the full amount
of
> the data and not the deduped data?  For example, the original 100GB
> deduped down to 20GB will be the full 100GB and not the 20GB? Or will
it
> be the 20GB, with Netbackup referring back to the index and/or base
data?
> >
> > Thanks,
> > Michael
> 
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