I have a problem about Symantec Backup Exec 2010 R3.
Example: when they use Symantec Backup Exec 2010 R3 to backup a file with size 1Gb, then their backup file is bigger 2Gb approximately 3Gb. The size of the backup file is double the size of original file.
If you are backing up compressed files using compression in the job, it can lead to a situation where it inflates the size of the file to larger than it should be.
I'd suggest checking that out first.
Also make sure that BE 2010 R3 is running the latest SP and patches, and if an upgrade is an option, consider upgrading to BE 15.