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SQL 2014 AG in-place upgrade to SQL 2016

Couple of questions regarding this topic.  Setup that I have is 4 nodes in Hyper-V.  2 same location and the others in different datacenters.  We use the systems databases for all logins.  So will need to migrate them as well.  

1.  When doing an in-place upgrade on an AG what is the rollback?  
2.  When manually failing over after the 3 secondary nodes are upgraded what happens?  
3.  Does it failover instantly or does it take it offline and upgrade?
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Justin Alcorta
Asked:
Justin Alcorta
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lcohanDatabase AnalystCommented:
Which of the two availability modes listed below are you using?

<<
Asynchronous-commit mode. This availability mode is a disaster-recovery solution that works well when the availability replicas are distributed over considerable distances.

Synchronous-commit mode. This availability mode emphasizes high availability and data protection over performance, at the cost of increased transaction latency. A given availability group can support up to three synchronous-commit availability replicas, including the current primary replica.
>>


The full upgrade guide is posted here https://msdn.microsoft.com/en-us/library/dn178483.aspx however these are few answers to your questions:


1. When doing an in-place upgrade on an AG what is the rollback?  
You can't really undo an in-place upgrade for single SQL instance alone never mind a full AG with 4 nodes so you would have to un-install everything and then restore your databases from a backup OR...image everything and snapshot storage but you will need to test this rollback scenario in order to rely on it SO...as they say here https://msdn.microsoft.com/en-us/library/dn178483.aspx 
<<‚ó¶Protect your data by performing a full database backup on every availability database>>


2. When manually failing over after the 3 secondary nodes are upgraded what happens?  
Not sure what you are talking about here but considering you have 4 nodes and didn't mentioned anything yet about the "last" one please note that in a "Rolling Upgrade" scenario you will "Always upgrade the remote secondary replica instances first, then local secondary replica instances next, and the primary replica instance last."

3. Does it failover instantly or does it take it offline and upgrade? -- it will "upgrade" indeed each SQL database on that instance same as you would do a backup/restore from old version to newer one so please test on largest database to estimate needed "downtime"

More about the topic is described here:
https://www.brentozar.com/archive/2015/02/patching-sql-server-availability-groups/
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Justin AlcortaEnterprise Systems AnalystAuthor Commented:
thank you for the information
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