Hello,
Have you installed the Exchange Agent on the media server.
Is it a local Backup or a remote backup?
Stop the anti virus service if its running during backups.
Also refer to the technotes given below.
(title) 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
(title) 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
Thanks,
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.