FAQs: Using Windows Server SAC in a Cluster; Choosing Between SAC and LTSC; Cluster Disk Witness

Three times a week (Monday/Wednesday/Friday), John Savill tackles your most pressing IT questions.

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In these FAQs we look at using the new semi-annual channel of Windows Server in a cluster, how we choose SAC vs LTSC and requirements around disk witness.

Q. Can I have a mix of 2016 LTSC and 1709 in the same cluster?

A. As with 2012 R2 and 2016, a cluster can have a mix of the 2016 LTSC (1607) and the first SAC (1709). Once all nodes are moved to 1709 you would use the Upgrade-ClusterFunctionalLevel cmdlet. The general guidance is a cluster can have n and n-1 versions mixed in a cluster as part of the migration to the new version.

Q. Can I use a Cluster Shared Volume for the cluster disk witness?

A. No. The Disk Witness is dedicated for the purpose of disk witness only. It cannot be a CSV nor used for additional purposes. It should be a dedicated LUN available to all nodes in the cluster and be 500 MB or larger. It must also be available to all nodes in the cluster. If you have a situation where a disk witness is not available to all nodes then use a file share witness that is accessible to all nodes or if using Windows Server 2016 you can use an Azure storage account via the cloud witness capability.

Q. Should I use Server Core is using SAC and Server with Desktop Experience if using LTSC?

A. Definitely not! The Long-Term Servicing Channel (LTSC) is the version of Windows Server that has the standard 5+5 years of support (five years of standard support, then five years of extended support) and is available in Server Core and Service with Desktop Experience installation options. The Semi-Annual Channel (SAC) is only available for Server Core (and also as a base OS image for containers as Nano Server).

The decision of Server Core vs Server with Desktop Experience should not be based on LTSC vs SAC. Yes, if you're using SAC you have to go Server Core so that is an easy decision however even if using LTSC you should still choose Server Core if possible. This provides lower footprint, reduced patching, reduced reboots, smaller attack surface and encourages remote management. Server with Desktop Experience should only be used if you need the graphical interface, i.e. a Remote Desktop Session Host. For pretty much all other scenarios, use Server Core.