The database backup failed message appears when backing up database manually using the Java tool in 8.x version of Console
The database backup failed. See the server log for details. No server.log entries are put into server.log
Netsight Console Extreme Management Center
The format of the database filesystem has changed in 8.x. This feature is no longer available with the Java tool.
Use of the Extreme Management Center backup tools is the method going forward. Use Administration->Backup/Restore instead. You can also automate backups under Administration->Options->Database Backup->Schedule Database Backup