Thank you for your reply,
I have already tested what you have suggested but problem is only with exchange email store using veritas backup exec. I can backup the entire server without the exchange within copule of hours, I have also used NTBACKUP to backup the store to a remote disk and all works fine and fast. I cannot think of any thing else.
It must be the protocols that Veritas 9.1 uses to backup exchange data. The only solution I can think of is to update to Symantec Backup Exec 12.5 with the Exchange option.