In data_engine probe log repeatedly getting the error "GetDatabaseDrive - select from 'master...sysdatabases' failed. Please check that the data_engine user has sufficient rights" .
What does this message mean ?
The data_engine user actually needs to be <db_owner>, just a db_datareader will not have access to the requested data, the values returned from the query run in the data_engine will return NULL, and you will get the error messages seen in the log.
The reason why these credentials is needed is that the data_engine queries system tables in the master database to figure out which drive the data file for the UIM database is located on, and it will check the available disk space and fire an alarm if there's less than 10Mb free space.
The rights described are the ones needed. If these rights aren't provided it will have no impact on the data_engine performance, the only thing that will happen is that the message will be written to the log every 5th minute.
It is possible to turn this message off by entering the raw configurator for the data_engine and setting the monitor_interval key to 0 (the default value is 300 seconds).