Hi Easwaran,
You may want to take a look at the following technotes.
Reasons why the data throughput rate can be slower than the theoretical maximum when backing up to tape media
http://support.veritas.com/docs/231488
How to correct slow backup performance, slow virus or pre-job scans, and agent initialization problems on fragmented Windows NT, Windows 2000, and Windows 2003 server partitions
http://support.veritas.com/docs/237444
Remote backups performed using agents (Agent for SQL, Agent for Exchange, Remote Agent, etc.) are unresponsive or extremely slow on particular machines.
http://support.veritas.com/docs/190828
What Backup Exec settings can be modified to reduce the amount of time it takes for a backup to run?
http://support.veritas.com/docs/249090
If you are using exchange refer to this technote too
Slow backup performance occurs when backing up Microsoft Exchange 2000 and Exchange 2003 servers between 1:00 am and 5:00 am.
http://support.veritas.com/docs/241858
There could be many possibilities why the data throughpur is slow. If fou can describe the situation precisely, it would help us isolate the issue.
NOTE : If we do not receive your reply within two business days, this post would be marked ‘assumed answered’ and would be moved to ‘answered questions’ pool.