Win2025 Hyper-V LUN format NTFS or ReFS?

[nd39475]

i have read on paper, ReFS is preferred, but I always read / have read ReFS issues online and in these forums. Considering a brand new Hyper-V environemnt, what id the offical and the unofficial stance for formatting LUN/Datastores? (iSCSI / Dell ME5084)
Thank you kindly.

[Mildur]

Hi nd39475,

If the question is about the right filesystem for your virtual HyperV disks, then I recommend asking this question in a Microsoft forum dedicated to technical Hyper-V topics.
Veeam Backup & Replication does not care whether VM disks are stored on NTFS or ReFS; you can protect VMs with either deployment type.

If you’re asking about a virtual Windows backup repository, then ReFS volumes are recommended for storing your backups.
However, please be aware of current ReFS stability issues; using a Windows Server 2025 as a ReFS backup repository will require a patch from Microsoft that has not yet been released: https://www.veeam.com/kb2792.

Additionally, do not mount the ReFS volume as a disk to your Hyper-V server and then create virtual disks for a repository VM. Instead, the iSCSI volume should be mounted directly as a volume on the backup repository VM.

Please keep in mind: using a virtual machine as a backup repository on your production Hyper-V host is not considered best practice. An attacker with access to Hyper-V Manager could potentially delete both your production workloads and all backups from a single point of management. It’s better to use a dedicated physical machine as a backup repository, preferably with immutability enabled. I recommend to check out our Hardened Repository.

Best,
Fabian