Azure backup or disk snapshot is better option for backup

 Hello,


I am new to the Azure cloud and have a few questions regarding the backup solution. 

 1. Azure backup and disk snapshot price are based on storage size? if yes I can see the disk snapshot size is exactly  same as the disk but the azure backup size is much lesser, I hope this is correct?

 2. I want to create VM backup for 7 days and after 7 days the first backup has to be deleted. Also, I want, only full backup for this VM then what will be the backup policy?


Regards