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.
This is a red herring, IMHO. In any integrated VTL worth its salt, this
is done with barcode matching:
1. You put physical tape LT00001 into the physical library (PTL)
2. VTL inventories PTL, finds LT00001
3. VTL adds LT00001 to inventory of VTL
4. NW backs up to LT00001
5. VTL sees LT00001 is full, copies it to real LT00001
5. NW ejects LT00001 from VTL, triggering eject of real LT00001
When you're done, NW thinks it copied to LT00001, and thinks it ejected
it, and that's what happened. If you expire/recycle LT00001, there
won't be any difference from what happened if the tape was physical from
the start.
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.
Again, this is no different than physical tape. Why would you be
expiring a tape that has backups on it you want?
Much easier (in my mind) to have NW stage the data from the virtual
tapes to a different physical tape. Doing that means that you can have
small virtual tapes and large physical tapes and not waste tape media
and according to recent discussion here
It's easier IF YOU CAN DO IT. What might stop you? Two things.
First, in the VTLs I've tested, there is sometimes a significant
performance difference between the copy speed of a
backup-software-managed copy and a VTL-managed copy. (It has to do with
the makeup of the backups on the tape. If there are a lot of files in
it, or if there are a lot of small incremental images, the copy can take
a lot longer if you do it via the backup software.) I had one customer
that tested the alternative, and found it to be about 20 times faster in
his environment to have the VTL make the copies.
Second, it's not like it's easy to automate making clones in NW,
especially in large environments. If you're good at scripting, you can
make it happen. If you're not, this is still NW's Achilles' Heal. BUT,
if you want to just back up to virtual tape, have those virtual tapes
become physical tapes, and then send those physical tapes offsite, you
can do that with no scripting -- if the VTL supports copying to physical
tape.
...increase performance on the VTL
Completely disagree based on what I've seen.
...and decrease the risk of virtual tape contention.
Again, I don't see where this is an issue.
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