Exchange 2010 DAG backup via netbackup

Hi Experts,

It is configured to take backup one mailbox DB on passive copy of one of the passive DAG node.  (without GRT, normal exchange backup)

I have triggered a full backup and the snaphost has completed but i dont see any byte movement in backup job.

I dont see any errors in detailed status of both parent and child streams. Nothing is showing under kilobytes in activity monitor and the time elapsed for this job is morethan a 30 mniutes.

Please let me know what should be reason ???????