OK, apparently related questions dont seem to address this directly. An exception reaches Elmah, maybe a repository cant reach a database, but then neither can Elmah reach that database. Even if they target different servers, maybe its a network problem.
Is there a way to configure fallback logs for Elmah for cases like this, e.g. a text file, message queue, email, sms, etc? If so, where do I start looking to do this, excpt for now the Elmah source code.
I am usually not so concerned about that: If the DB is not running then my application is not running and I have no exceptions to log anyway. But if this is an issue for you then you could consider to use the XmlFileErrorLog.
As far as I can tell you cannot use more then one log destination and there is nothing like a fallback. You could however configure email notifications, but then you would get all exceptions by email as well.
Here is quite a nice article about elmah.