If you are using Client side backup option while taking backup, you can use client direct restore, It is increasing restore speed.
If you are not using Client side backup or any option, you can increase channel and media and client network as well you can see better results.
As I know, depend your version database Oracle for you can increase numbers of channels, ask for your DBA, so another thing if backup was done in 4 channels is not possible you increase restore for 6 channels, right? this about Oracle not relation with Netbackup.
several notes to this thread:
- you can generally use a different number of RMAN channels for restore than for backup (both less and more). When a backup device is a disk, it ia easily achievable, when the device is tape, you can be naturally limited by number of drives and how the data are spread on individual tapes. So only some channels can be active, rest can remain queued
- generally, backup system is not the only point which is responsible for backup/restore speed. Entire environment contributes - network, storage, source device, target device. If you have a bottleneck somewhere here, number of channels wont help you
- client side dedup is not a mandatory condition for client direct restore. See here https://www.veritas.com/support/en_US/doc/25074086-127355784-0/v95644490-127355784