Fileserver with million files , backup is taking more than 80 hours

I have a fileserver cluster windows 2008 with million files , we are using netbackup verions 7.6 with HP StoreOnce Catalyst version 2.1 , Full Backup is taking around 80 Hours + , and incrmental is taking around 14 hours + , i am searching for a solution to minimize the backup windows size for the full back less than 48 hours and the incrmental less than 8 hours , please can anyone help me in that , Accelerator is not supported in storeonce so i need another soluiton, please help ASAP