SLP network traffic
What path does the data take if it is duplicated with SLP?
Is it transferred directly via SAN between the involved storage boxes? Or is it SAN from source storage to media server of source STU, and then LAN to media server of target STU, and then SAN again to target storage?
In that case traffic will go over LAN when replicating data with SLP.
You want a very strong network with enterprise grade switches when working with Netbackup. Switch ports need to be non-blocking.
Also, you don't want to write and read to the same disk pool at the same time using spinning disk. There should be time for writing (backup) and reading (replication).
There is a lot of good information in the "NetBackup™ Backup Planning and Performance Tuning Guide"
https://www.veritas.com/content/support/en_US/doc/21414900-146141073-0/v19525319-146141073