Q. Should I use NTFS or ReFS for my Windows Server 2016 Cluster Shared Volumes?
A. Always use NTFS for your Cluster Shared Volumes even though Hyper-V VMs are now supported on ReFS in Windows Server 2016. The only exception is when using Storage Spaces Direct in which case you should use ReFS. A big reason for using NTFS is that when using ReFS for Cluster Shared Volumes it always runs in file system redirection mode which means all I/O is sent over the cluster network to the coordinator node for the volume (this is why RDMA network adapters are recommended with Storage Spaces Direct for the cluster network) rather than nodes using Direct IO to access disks directly. Also remember that with Storage Spaces Direct there is no shared storage anyway so all access is essentially redirected.