We will setup an experimental mysql instance alongside tendril, initially to store database backup statistics. This is mostly experimentation needed to have clear the requirements and main blockers of the goal. However, it could also become in the future a source of truth for other tasks, out of the backup scope.
The relationship with prometheus is not yet clear- but this doesn't discard the usage of prometheus entirely, but just complement it (mysql being used to control the current state and prometheus, gather historical statistics?).