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I am running Windows update on my SQL Servers (which are in a Principal-Mirror partnership, in High Safety mode).

I am starting with updating the mirror and I was wondering, to increase safety, should I pause mirroring and stop SQL Server Services and then run Windows Update? Or is this totally unnecessary?

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Suggest you to PAUSE mirroring and then patch the windows.

Ideally, I would follow below approach :

  • If you have a witness configured, turned it OFF as during the patching, if sql server service is restarted or the server reboots, then a witness will initiate a failover.

    ALTER DATABASE [db_name] SET WITNESS OFF

    • Always patch the current mirrored server, so if things go wrong, then you atleast have your principal ON.

      • Reboot the mirror server (if necessary)

    • Now failover to the newly patched mirror server. Run below T-SQL on the current Principal server ALTER DATABASE [your database] SET PARTNER FAILOVER

    • Once the failover is completed, patch the current mirror (which was originally primcipal)

      • Reboot if necessary

    • Now failback to the original principal server.

    • Add back the witness (if removed from step 1)

      ALTER DATABASE [db_name] SET WITNESS = 'TCP://[FQDN]:[port_number]'

    • As a saftey measure, run DBCC CHECKDB on your databases.

From BOL :

enter image description here

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  • I thought if Witness and Mirror are unavailable, Principal will refuse all transactions? – Dina Feb 5 '14 at 20:58
  • @Dina that is not true. Why would Principal refuse connections ? Readup on database mirroring to avoid any confusion. – Kin Shah Feb 5 '14 at 21:03
  • Right, I'm confusing myself with this scenario: sqlblog.com/blogs/tibor_karaszi/archive/2010/04/16/… – Dina Feb 5 '14 at 21:09
  • @Dina Good point and I can see why the confusion happens. The scenario that the article describes is called split-brain scenario. Also, if you see my answer, I have explicitly told to turn-off the witness. HTH. – Kin Shah Feb 5 '14 at 21:16
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Normally if the updates are SQL based (and certain conditions are met), the program will handle the stopping/starting of related services.

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