I'd say #1 is the best way, since you stay in full control.  #2 will tie up
the "MIGPROC" number of drives in the old library, making control harder.

If you can keep both type of libraries for a while, you can just point the
new data to the 3494's, wait for expiration to clean up most of what is in
the old library (which should take around the Retain Extra Versions number
of days), then do MOVE DATA's on the remaining tapes in the 3575's.  To
reduce the number of in-use tapes in the 3575's, you can drop the
reclaimation threshold, so TSM will consolidate the data on the fewest
number of tapes (reducing the number of MOVE DATA's you need to run).

Nick Cassimatis
nickpc AT us.ibm DOT com

"I'm one cookie away from happy." - Snoopy (Charles Schulz)