[Veritas-bu] DSSU vs VTL

David Rock dave-bu at graniteweb.com
Mon Mar 7 13:04:40 CST 2005

* Lee, Kenneth (SBS US) <kenneth.lee at siemens.com> [2005-03-07 13:38]:
> I have some general questions regarding NetBackup's Disk Staging Storage
> Unit (DSSU) and Virtual Tape Library (VTL):

We are actually using both in different envrionments.

> 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?

Virtual tape looks like tape drives to NBU, so you can do things like
use SSO to share "drives" between media servers. A DSSTU is restricted
to the media server that actually has the disk space. Some VTL solutions
also have other skills outside of NBU to handle offline tape creation
that allow you to offiste "originals" with vault but actually create the
physical tape directly, freeing up NBU resources.

> 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? 

This can vary, but NBU would see these as additional tape drives,
although some allowances can be made. YMMV

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

It depends on your needs. Smaller installations (e.g. not using SSO) are
great for DSSTUs and it is a very effective way to offload backups to
physical tape. If you need to use SSO and share resources (e.g. can't
afford disk on every media server), then VTL is a good option. 

I think DSSTUs work better out of the box for managing image expiration
and other issues like that, but both DSSTUs and VTL options make you
more aware of how your policies are set up (long initial retentions are

David Rock
david at graniteweb.com
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