I have opened simulaneous posts here and here as I am attacking our RMAN issue from all angles. After much thought and investigations, what resolved our issue is providing a second network card for the other VLAN.
Initially we started with a flat network and hence our server only have a single NIC. As we progress to using VLANs, and adding restrictions between VLANs, the server connectivity was left behind. So we were having VLAN 10 and VLAN 12 going to a single NIC which is on VLAN 10. As soon as we separated the two VLANs into their respective NICs, backup transfer rate went up more than double! From 10 to 12 hours of trying to backup a 2TB database it went down to just 02:16 hours.
Network team is silent as to why this made an improvement.
