Hi Prajith,
if you have access to the SAP Note System you can use the following sapnote 1676903 which tells how to analyze and optimize the backups.http://service.sap.com/sap/support/notes/1676903
You do the analysis with the help of Database Analyzer Expert files.
My experience is that in most cases I could optimize backups by using a parallel medium instead of a single medium.
Regards, Christiane