vFC storage connection WWN pool issue

Sofie Meier 0 Reputation points
2026-08-26T11:47:29.7566667+00:00

Hi guys

May I know if anyone here has encountered a problem when adding new VMs with vFC storage connections, where the process fails and shows “No available WWN addresses in the pool”? I’m trying to understand whether this limitation is due to the default vFC SAN adapter WWN range configuration or something else.

How can we modify the default WWN ranges for vFC adapters without disrupting currently running VMs or causing storage path re‑enumeration issues ?

Windows for business | Windows 365 Enterprise
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  1. Allan Solomon Mejia 6,240 Reputation points
    2026-08-26T20:41:14.1066667+00:00

    Hello @Sofie Meier

    The error “No available WWN addresses in the pool” in this case relates to Hyper-V Virtual Fibre Channel (vFC) WWN allocation, not the physical SAN adapter's WWN range.

    Hyper-V assigns WWNs to each virtual Fibre Channel adapter. Microsoft documents that each vFC adapter can use automatically generated WWNs or manually assigned WWNs. For Live Migration, Hyper-V maintains two WWN sets (Set A and Set B) for each virtual Fibre Channel adapter.

    Before changing anything on the physical HBAs or SAN, check the vFC configuration of the affected VM and existing VMs:

    Get-VMFibreChannelHba -VMName "<VMName>" |
    Format-List *

    You can also review the virtual SAN configuration:

    Get-VMSan

    If automatically generated WWNs are exhausted or allocation is failing, you can configure WWNs explicitly for a new virtual Fibre Channel adapter rather than modifying WWNs already assigned to running VMs. Microsoft specifically supports manually assigning WWNs when configuring a vFC adapter.

    I would not change the WWNs of existing production VMs just to resolve this. Existing WWPNs can already be referenced by Fibre Channel zoning and LUN masking, so changing them can cause the SAN to see the VM as a different initiator and disrupt storage access.

    Also verify that:

    • The physical FC HBA supports NPIV and has current drivers.
    • The SAN fabric has NPIV enabled.
    • The Hyper-V Virtual SAN is mapped to the expected physical FC ports.
    • The new VM's WWNs are unique and correctly included in SAN zoning/LUN masking.

    Microsoft documents that an NPIV port is created when a VM using vFC starts and removed when it stops. This is separate from changing the physical HBA's WWN.

    Therefore, I wouldn't modify the physical SAN adapter WWN range. First inspect the Hyper-V vFC WWN assignments and determine whether the problem is with automatic WWN allocation. If necessary, manually assign unique WWNs to the new vFC adapter, while leaving existing VM WWNs unchanged.

    Sharing these references with you:

    Hyper-V Virtual Fibre Channel in Windows Server

    Implement Hyper-V Virtual Fibre Channel

    Please "Accept the Answer" if this information helped you. This will help us and others in the community.

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