ReFS cluster size with Veeam Backup & Replication: 64KB or 4KB?

There has been a lot of discussions about ReFS 3.1 after Veeam released its version 9.5 with support for the block clone API. With this integration between the two product, users can now design a repository that combines the speed of a non-deduplicated array, with some important space savings that usually belongs to those dedicated appliances. We have seen many many discussions in our Veeam forums, and I also published two articles on this topic you may want to read: Windows 2016 and Storage Spaces as a Veeam backup repository and An example for a Veeam backup repository using Windows 2016.
Now that people are starting to use ReFS, another question has risen: which cluster size should I use? 64KB or 4KB?

An example for a Veeam backup repository using Windows 2016

In my previous article Windows 2016 and Storage Spaces as a Veeam backup repository I talked about the advantages that Veeam Backup & Replication can bring when combined with Windows Server 2016 and the new ReFS 3.1 filesytem. Several people have asked already about some practical examples about how to design a solution using these technologies, so I thought it was time to give you one storage design.

Windows 2016 and Storage Spaces as a Veeam backup repository

As Microsoft Windows 2016 is now finally generally available, people are starting to seriously looking at its features, and no doubt S2D together with the new ReFS 3.1 is one of the hot topics. I’ve first of all updated my lab with the final version of Windows 2016 in order to have my cluster in a “stable” state, than I started to focus on the different topics related to Windows 2016 and its usage as a Veeam repository. And I started to ask How can we leverage ReFS BlockCloning and Storage Spaces to make Windows 2016 the best solution for Veeam repositories? What about Storage Spaces Direct?”.