MicrosoftHi Hassel-z you might want to join azurestackhci.slack.com to receive answers. Feel welcome. It's a serious technical community for S2D and likewise Azure Stack HCI.
Generally S2D works with direct and local attached storage SAS, NVMe, unlike unclustered Storage Spaces, which could even support USB.
ReFS is the file system of choice for S2D.
By-Design only the CSV owner (coordinator node) uses Direct IO.
It's a good practice to create one or better two CSV per physical node and try to align VMs to the node and CSV owner for 100% of performance in highly write intensive workloads (IOPS).
All other traffic is always redirected, but then using a storage intent for SMB multichannel and at best RDMA with RoCEv2 for minimal penalty for the redirection.
See my comments above why ReFS CSV may not be used for SAN / NAS in the same fashion.
You can learn more about this in learn.microsoft.com on the topics ReFS, Storage Spaces Direct, Azure Stack HCI networking requirements and concepts (they are similar to S2D).
Admit the S2D docs might be cluttered or appear outdated, it is in active development with another round of major advancements coming in Windows Server 2025.
You might want to learn more about the upcoming changes in the Windows Server 2025 summit recordings on techcommunity.microsoft.com.
You can also leverage Windows Server 2025 b26100 already for testing.
You can also test and learn more S2D and Azure Stack HCI with mslabs on GitHub.
Note: Domain Controller for mslab still require WS 2022 at the moment. WS 2025 preview works for all other VM types.
