1). Login to SSH as root.
2). Open cpanel.config file through vi editor
# vi /var/cpanel/cpanel.config
3). Now, look for
disk_usage_include_sqldbs=0
4). You have to change the value to 1 from 0
disk_usage_include_sqldbs=1
5). If this parameter is not present in the file then you have to add it.
6). Save the file and execute the following command:
# /scripts/update_db_cache
It may take some time to get it fixed depending on the number of users with databases. Once it is done then you will be able to see database disk usage show up accurately in cPanel.