Have you recently encountered the MSSQL 18456 Event? I’ve seen this come up in quite a few migrations after Microsoft Lync 2013 is installed and pools are paired. Since I couldn’t find much about MSSQL 18456 on the internet, I thought I would share my findings for everyone else who has experienced an endless number of MSSQL 18456 information events.

Once you encounter the MSSQL 18456 information event, fill the application event log with the message: “Login failed for user 'DOMAINSQLSERVERNAME$'. Reason: Failed to open the explicitly specified database 'xds'. [CLIENT: IP Address]”. This issue can occur if the Lync 2013 pools were set up and paired first, and the CMS moved later to one of the pools. If you see the message above related to your backup pool, the simplest thing you can do is remove the pairing from the topology, publish, then reestablish the pairing and republish. Another alternative is to create the database via the PowerShell using this command: Install-CsDatabase -CentralManagementDatabase -SQLServerFQDN-SQLInstanceName.

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