Solved! Go to Solution.
Pretty much as Marianne says ....
You cannot specify a target tape, you specify the target pool, so just make sure the LTO8 tapes are in their own unique volume pool.
bpduplicate -id <media id to copy> -dstunit <destination storage unit> -dp <destination volume pool>
bpduplicate -id TAPE1 -dstunit tape_stu -dp nbu-duplicate
Also, remember that no hardware is compatible with both LTO3 & LTO8, so you'll need at least two tape units, one which can read LTO3 media (could be LTO3, LTO4 or LTO5 drives) and another that could write LTO8 (only LTO8 tapes can write on LTO8 media right now). You should be able to duplicate from the old media to disk, and from there to the new media.