WP Backup Complete is a complete backup solution for WordPress. The plugin will backup the WordPress database as well as the file system.
Like most backup plugins, WP Complete Backup depends on server conditions. Ensure that your server has write permissions to the /wp-content/plugins/wp-complete-backup folder.
Also, be mindful of server disk space. If you have a large site, the backup may exceed your available disk space. Try doing just a database backup first. If a database-only backup works, it may be a sign that a combined backup exceeds your server's available disk space.
The database backup is in SQL-Dump format and is located in /wp-content/plugins/wp-complete-backup/storage ... Inside the storage folder is another folder named after the UNIX timestamp of when the backup was created. The database SQL file is located in that folder.
No, each backup will only include the storage location for that backup. Previously stored backups will not be included with new backups (this is so a backup file doesn't exponentially grow in size).