Why do you really want to use VTL at all?

Using a DD you are talking to very fast network-attached AFTDs where NW 8 
clients can even use new technologies like Flexible Blocksize & Direct File 
Access. The data rates which you achieve here are amazing, especially when you 
stream data from various clients to multiple AFTDs and - at the same time - 
simulteanously clone data from these devices to tape (if needed at all). Only 
in rare cases, the clients must have faster NICs than 1GbE but of course that 
also depends on the data rate you must achieve.

My opinion is to avoid VTLs whenever possible. Yes, you have fast SAN access 
but IMHO this is the the only benefit. You really force a disk to behave like a 
tape and in general, you add an additional, unnecessary 'layer' which limits 
the flexibility B2D would offer. And of course it is a an additional component 
which potentially might cause trouble. Just avoid it!

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