For reference, VTLs are licensed based on their size not on the number of 
virtual tape drives you create. 

John Nardello
T-Mobile: Enterprise Systems Backup Group Technical Lead
"Your backups are only as good as your restores."


-----Original Message-----
From: veritas-bu-admin AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-admin AT mailman.eng.auburn DOT edu]
Sent: Monday, March 07, 2005 6:55 PM
To: Lee, Kenneth (SBS US)
Cc: 'veritas-bu AT mailman.eng.auburn DOT edu'
Subject: Re: [Veritas-bu] DSSU vs VTL


On Mon, Mar 07, 2005 at 01:38:22PM -0500, Lee, Kenneth (SBS US) wrote:
> I have some general questions regarding NetBackup's Disk Staging Storage
> Unit (DSSU) and Virtual Tape Library (VTL):
> 
> 1.    If DSSU gives you the ability to write to disk and at a later time,
> migrate the backups to tape, what is the advantage of using Virtual Tape
> Library?

DSSU doesn't work very well yet.  It has certainly been somewhat buggy
in not cleaning up after itself.  It's getting better every release and
I would expect that trend to continue.

VTLs typically compress writing data to disk.  DSSU doesn't.  That
doesn't mean that DSSU won't be compressing in the next release of
NetBackup though - that's an easy feature for Veritas to add anytime
they want to.  In the short term, though, you could potentially need
half as much disk space in a VTL than you would in a DSSU.

> 2.    If I was to implement VTL, how will this impact the license cost
> from Veritas?  Would cost go down, up, or stay the same? 

A virtual tape drive looks just like a real tape drive so you need to
license it in addition to your physical tape drives.  If you run other
products on top of NetBackup that are licensed based on number of tape
drives or robots, you may need to additional licensing (and maintenance
fees) on those too.

> 3.    Is one method better then the other (DSSU vs VTL)?

DSSU is free today.  VTLs you need to pay more money for.  It's up to
the VTL vendors to convince you that you're getting better value for your
money spent on VTLs than you could get spending your limited money on
something else in your data center.  They haven't convinced us yet.

-- 
Ed Wilts, Mounds View, MN, USA
mailto:ewilts AT ewilts DOT org
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