Real Zero-Downtime Patching in SharePoint 2016

It is exciting to have Zero-Downtime Patching (ZDP) capability in SharePoint 2016. However, it requires more effort than most of us might have initially thought. While it is straightforward for other components, it requires a bit more care on Distributed Cache.

Distributed Cache doesn’t support High Availability the way that other services do. While multiple Distributed Cache servers in your SharePoint farm can help distribute the load, the data cached on each Distributed Cache server is NOT replicated to the other Distributed Cache servers. If a Distributed Cache server unexpectedly goes down, the data cached on that server will be lost. That means if you install patches and upgrades a Distributed Cache server without gracefully shutting it down, you will cause data lost!

One may argue that if there are three Distributed Cache hosts on the farm, there will be high availability for the Distributed Cache as AppFabric has as cluster quorum model. That is not true as SharePoint is not using that model!

Therefore, if you have workloads that heavily depends on Distributed Cache and have high availability requirements, add Gracefull Shutdown of the Distributed Cache Service into the patching process to have true Zero-Downtime.

Gracefully shutdown DCS: https://technet.microsoft.com/en-us/library/jj219613.aspx#graceful

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