Microsoft's Windows Server 2016 will introduce the ability for customers to upgrade Windows Server 2012 R2 clusters to the new version without taking the cluster offline and without the need for a second cluster to take over while the upgrade proceeds.
Windows Server 2016 is still slated for release sometime later this year, and is widely expected during the third quarter. The most recent pre-release version, Windows Server 2016 Technical Preview 5, was made available to testers at the end of April.
Microsoft has now detailed how an upcoming feature will enable customers to migrate any Windows Server 2012 R2 cluster to Windows Server 2016 with minimal impact. This can even be done with zero downtime for server clusters running physical Hyper-V and Scale-out File Server (SoFS) clusters, the firm claimed.
Known as the Cluster OS Rolling Upgrade, this feature introduces a new concept called Mixed-OS mode, which allows customers to start with a Windows Server 2012 R2 failover cluster and add Windows Server 2016 server nodes to the cluster, Microsoft said.
Using this and a sequential upgrade process, customers can migrate each server to Windows Server 2016 one by one, without having to take the entire cluster offline. Once the upgrade is complete, customers will then be able to take full advantage of the other new capabilities Microsoft is delivering with Windows Server 2016.
"After all nodes in the cluster have been upgraded to Windows Server 2016, the administrator uses the Update-ClusterFunctionalLevel cmdlet to commit the cluster to permanently running Windows Server 2016 nodes only - at which point the new Windows Server 2016 features become available," said Rob Hindman, Microsoft's senior programme manager for Windows Server, on the Windows Server Blog.
Hindman explained that zero downtime applies only to Hyper-V and SoFS clusters because a Hyper-V cluster makes use of VM Live Migration so any virtual machines will keep running during the process, while SoFS makes use of Continuously Available file handles which can move between cluster nodes without any data loss.
"Other cluster workloads like SQL Server AlwaysOn Failover Cluster Instance and SQL Server AlwaysOn Availability Groups can be upgraded with minimal downtime which is equivalent to failover time," he added.
Meanwhile, virtual (guest) clusters using Shared VHDX (shared virtual hard drives) need to be logically detached from shared storage before the upgrade and reattached after the upgrade process has completed.
"We've worked closely with many customers using Windows Server 2016 Technical Preview to ensure that Cluster OS Rolling Upgrade delivers the deployment agility that they need, reducing the time and cost needed to upgrade to Windows Server 2016," Hindman said.
Customers can download the Windows Server 2016 Techncial Preview for evaluation from Microsoft's TechNet site.
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