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Within this scenario, the main and backup server are using the same SQL server instance. The following figure shows the situation where the main server is online:
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In this situation, the main server is connected to the SQL instance. The backup server is inactive and thus not connected to the SQL instance. Now, consider that the main fails and the backup server is getting active. In this case, the backup opens the connection to the single SQL instance:
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This solution has the advantage that is easy to configure. In addition, only one SQL instance is required and no additional license fees for an SQL synchronization are necessary. The drawback is that the SQL instance is a single point of failure. If the SQL instance fails, the data is not available for BMS functions like reporting. To increase the reliability of a single SQL instance, hardware redundant server systems or fail-safe virtual machines can be used.
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