[Francis Swasey wrote]

"If I was to go with a VTL, I would not allow the VTL to write the 
physical tapes.  I would have NW control the physical tapes as well as 
the virtual tapes.  I do not want to get into the situation where the 
VTL has copied a virtual tape (VT00001) out to a physical tape (VT00001)

and then NW recycles that tape in the VTL and uses it again.  NW has now

lost track of the data that is on the physical VT00001.    If you can 
keep NW from ever recycling the virtual tapes so that it never loses 
track of the data on the physical tapes, then you'll be ok."

This is an excellent point, and is exactly the reason that EMC offers an
embedded NetWorker storage node as an option in their EMC Disk Library
(EDL).  By using this feature, in concert with NetWorker's standard
cloning functionality, you have the VTL server make the clones directly
from the virtual tapes.  You don't need to burden a 'production' storage
node with this task, and you don't need to pull the data across the SAN
to the production storage node, and then write it out to the target
device.

Also, again using standard NetWorker cloning functionality, you can
clone from virtual tape to a locally-attached physical tape, as well as
cloning to a remote storage node (over IP) to virtual or physical tape
in the remote location (where that remote storage node could be either
embedded in another EMC Disk Library, or just another storage node in
the environment).  Standard cloning functionality also allows you to
change the media tape during the clone operation, so you don't have to
have the same physical tape drives as the virtual tape drives used to
create the original backup.  And so on and so on.

Finally, EMC has made several enhancements to make the EDL and NetWorker
work well together.  Examples include automatically turning off the
autochanger resource mechanical delays (virtual devices have
near-instantaneous load times, of course), storage node affinity changes
(a clone source tape will be dismounted from the production storage node
and re-mounted on the embedded storage node before cloning begins) and
the NetWorker ability to use persistently-named devices with the EDL
embedded storage node.

If other VTL products have similar features, please speak up; I think
many of us would like to hear more on this topic.

Thanks
tl

To sign off this list, send email to listserv AT listserv.temple DOT edu and 
type "signoff networker" in the body of the email. Please write to 
networker-request AT listserv.temple DOT edu if you have any problems with this 
list. You can access the archives at 
http://listserv.temple.edu/archives/networker.html or
via RSS at http://listserv.temple.edu/cgi-bin/wa?RSS&L=NETWORKER