Symptoms
1. Scheduled Plesk backup is enabled.2. FTP is used as storage for backup files
3. FTP is configured correctly
4. Option If backup file exists is set to Generate Next file name
According to these settings Plesk backup should upload created backup files onto specified FTP server and generate new file names for files that already exist. But Plesk keeps overwriting the existing files.
Resolution
This problem has been solved in Plesk version 8.1.1. Consider upgrading Plesk to the latest version.