Difference between Application Size and Media Size

Hi @Jinmi , 

Size of Application

The amount of application data that has been protected during this job. The amount of compression possible on the data is also displayed.

Data Written (Media Size)

Size of the data stored on the media. This is the size of the data after deduplication and compression, if employed. This amount also includes metadata information, so in some cases, it could be larger than the actual size of the backed up data. (For information on data written size for HPE StoreOnce Catalyst Library , see HPE StoreOnce Catalyst Library - Frequently Asked Questions.)

Please refer to this link for more information

https://documentation.commvault.com/11.22/expert/6490_job_history_online_help.html