How Is RDS for MySQL Backup Data Charged?
All the RDS full and incremental backup data is stored in OBS. RDS provides free backup storage space of the same size as your purchased storage space. For example, if you purchase a DB instance with 200 GB of storage, you can get an additional 200 GB of backup storage. The first 200 GB of backup data is free and the backups in excess of that 200 GB is billed on a pay-per-use basis. For pricing details, see Product Pricing Details.