SQL Server availability group asynchronous secondary extended downtime...suspend necessary?



  • Our asynchronous secondary replicas will have some extended downtime over the next few weeks. 3-4 hours one night then 2-3 days a few weeks later. I know the primary replica logs will keep growing while the secondary replicas are down. I'll keep an eye on the Log drives to add disk space if they get close to filling up.

    Should I suspend data movement on each secondary database before powering down the secondary VMs, or will the vm being offline serve the same purpose? Any differences in the way the primary will function if the secondary is suspended vs. powered down without suspending?

    The AGs/clusters should stay online due to the primary + file share witness providing quorum, correct?

    Also, our apps connect to the primary's DNS name (or an alias), not via the AG/cluster name. When the secondaries come back online, they should start catching up, right? Thanks!



  • If you're going to take the asynchronous replicase offline for a few hours, it should be acceptable to suspend data movement first, perform the maintenance you need to do, and resume data movement when the secondary replicas are back online. I'd continue to monitor transaction log growth on the primary replica during that time. Though that's a fairly short time period to fill up a transaction log.

    When you start talking about multiple days, I'd plan to remove the secondary nodes from the availability group entirely during that time. That is, unless you plan on monitoring the transaction log 24x7. Otherwise, there's too much that could go wrong. In theory, you could predict the log growth over 3-4 days. But who's to say there's not a random job that runs once a month, or once a week, that's going to run right in the middle of your 3-4 maintenance window, and it hits the log hard at 3am, when no one's watching. Just don't take the chance. It's too easy to add the nodes back to the availably group later.

    As for quorum, we can't answer that without knowing your quorum configuration. How many production replicas do you have compared to DR? Where is the file share is located. Assuming DR has no voting rights, you should be fine.




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