(vSphere 5.1) Windows 2012 VM running Oracle DB freezes during netbackup causing heartbeat failure

I'm experiencing OS freezing during netbackup causing heartbeat failure from my application to database, thus causing application to shutdown. After days of troubleshooting, I realise that the disk latency shoots up to as high as 21 ms and when it happens, the OS stops responding for a while even I was connected by VM console. May I seek the community's advice on how to mitigate the issue?