A few weeks ago one of our clustered server nodes blue-screened and when it came back on SQL refused to start. I started digging in and this is what I found in the Event Log: “Script level upgrade for database ‘master’ failed because upgrade step ‘sqlagent100_msdb_upgrade.sql’ encountered error 200, state 7, severity 25.” Immediately I started to suspect a corrupt master database. And I found this in the SQL Error Log:

Creating procedure sp_sqlagent_get_perf_counters…

Error: 468, Severity: 16, State: 9.

Cannot resolve the collation conflict between “SQL_Latin1_General_CP1_CI_AS” and “Latin1_General_CI_AS” in the equal to operation.

Error: 912, Severity: 21, State: 2.

Script level upgrade for database ‘master’ failed because upgrade step ‘sqlagent100_msdb_upgrade.sql’ encountered error 200, state 7, severity 25. This is a serious error condition which might interfere with regular operation and the database will be taken offline. If the error happened during upgrade of the ‘master’ database, it will prevent the entire SQL Server instance from starting. Examine the previous errorlog entries for errors, take the appropriate corrective actions and re-start the database so that the script upgrade steps run to completion.

Error: 3417, Severity: 21, State: 3.

Cannot recover the master database. SQL Server is unable to run. Restore master from a full backup, repair it, or rebuild it. For more information about how to rebuild the master database, see SQL Server Books Online.

SQL Trace was stopped due to server shutdown. Trace ID = ’1′. This is an informational message only; preser action is required.

I started going through the steps to restore master. I was able to start the server in single user mode, yet I could never get in as the single user. Something seemed to always be taking the connection before I could get in.

I had a long, long conversation with the #sqlhelp folks on Twitter about this. All of these guys and gals were tossing out help: @sqlinsaneo @kbriankelly @darrelllandrum @rusanu @DBArgenis @Kendra_Little @mrdenny @Bugboi @SQLSoldier. We stopped all services that were known to connect, stopped the browser service, changed the port, only allow IP connections, paused the cluster node I was working on, and still I was getting an error that only one admin was allowed at a time in single user mode.

Since I was getting nowhere fast, I decided on a different tact, namely to rebuild master then recover from backup. Rebuilding master was a fairly quick process. An important note about rebuilding master is that is also rebuilds msdb. Now I had two databases to recover from backup. Once the rebuild was complete, I was successfully able to start the service in single user mode  and was able to connect (yay!!!). Now I could restore a backup of master, restart SQL normally and restore msdb. I finally had a running instance 2.5 hours later.

Important lessons learned from this experience:

• If single user mode isn’t working and you have a good backup of msdb, rebuild then recover. Rebuilding might fix some issues and get you on the road to recovery quicker.
• Collations of all the system databases really should match. This whole issue was because of a collation conflict between master and msdb.