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We're planing to have two SQL servers updated by synchronous database mirroring. This will include a third environment configured as a witness server.

For standard windows patching - what order should we patch / reboot the servers?

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The order would go like this:

  1. Update the secondary server (the one that is not currently serving connections)
  2. After it reboots, do a controlled mirroring failover to it
  3. Update the primary server (which at this point is no longer serving connections)
  4. After it reboots, you can do a controlled failover back to it if you want, but you don't have to. You can leave the connections running on the secondary box.
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Thanks Brent, how does patching the witness server fit in? – SuperCoolMoss May 18 '09 at 11:39
If the witness server isn't involved in anything else whatsoever, then you can do that first. I usually see the witness being involved with other SQL Server activities, though - for example, it might be a mirroring partner for another primary server, so it can't be rebooted willy-nilly. If you're lucky enough to have a dedicated mirroring witness that does nothing else, then you can get it done first, but it doesn't matter whether it's first or last. – Brent Ozar May 18 '09 at 11:49
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Be careful just leaving the connections running on the secondary box if you don't have a license for it. It's only free if you fail back to the original principal within 45 days. – Paul Randal May 18 '09 at 14:20
Great point, +1 on the comment. Didn't know about the 45-day limitation - I thought it'd be even shorter than that. – Brent Ozar May 18 '09 at 14:24
Thanks Paul and Brent - Am I correct in thinking if all user databases are failed over to the secondary (no active connections to user databases on primary) then the 45 day limitation can be ignored? – SuperCoolMoss May 18 '09 at 17:47
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