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Cluster Functional Level

Lucas Peñaloza 41 Reputation points
2025-06-10T19:03:32.66+00:00

Dear;

I have to Upgrade a Windows Server failover cluster with a cluster OS rolling upgrade!!!.

My question is:

It is necessary to execute Cluster Functional Level Update?.

How long can the failover cluster run in mixed-OS mode?.

If the Cluster Functional Level isn't updated, is it a risk? Or can it function perfectly?

Today, the Planning is to update only the Cluster Nodes.

Windows Server High availability Clustering and high availability
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  1. Andrew Li 155 Reputation points Microsoft External Staff
    2025-06-11T07:17:13.44+00:00

    Hi Lucas ！

    Thank you for contacting the Microsoft Community!

    I noticed that you are performing a rolling upgrade on your cluster. For information on this topic, you can refer to the following link: https://learn.microsoft.com/en-us/windows-server/failover-clustering/cluster-operating-system-rolling-upgrade

    After you have updated all the nodes within the cluster, you must execute this command within 4 weeks: Update-ClusterFunctionalLevel to get your cluster out of the mixed OS state. This description can be found in the documentation.

    If this time is exceeded, your cluster may encounter unknown errors such as being unable to be managed through the cluster manager. For best practice, please perform this action immediately after the update.

    Best Regrads，

    Andrew

    1 person found this answer helpful.

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  1. Lucas Peñaloza 41 Reputation points
    2025-06-11T17:41:04.5666667+00:00

    Andrew;

    Thanks for the information!!!.

    The infrastructure is Windows Server 2016, we must upgrade to Windows Server 2019 or we can do it directly to Windows Server 2022?.

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