Considerations for using software iSCSI port binding in ESX/ESXi

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Purpose
This article provides information on when to use and when not to use iSCSI port binding. For information on how to configure port binding, see the storage guide for your version of ESXi/ESX.
Resolution

Port Binding

Port binding is used in iSCSI when multiple VMkernel ports for iSCSI reside in the same broadcast domain and IP subnet to allow multiple paths to an iSCSI array that broadcasts a single IP address. When using port binding, you must remember that:
  • Array Target iSCSI ports must reside in the same broadcast domain and IP subnet as the VMkernel port.
  • All VMkernel ports used for iSCSI connectivity must reside in the same broadcast domain and IP subnet.
  • All VMkernel ports used for iSCSI connectivity must reside in the same vSwitch.
  • Currently, port binding does not support network routing.

When not to use port binding

Port binding should not be used when:

  • Array Target iSCSI ports are in a different broadcast domain and IP subnet.
  • VMkernel ports used for iSCSI connectivity exist in a different broadcast domain, IP subnet and/or vSwitch.
  • Routing is required to reach the iSCSI array.
  • Software iSCSI Port Binding is also contraindicated when LACP or other link aggregation is used on the ESXi host uplinks to the pSwitch, Limitations of LACP in VMware vSphere 5.5 (2051307)

    Example


    In this sample scenario, there are multiple VMkernel ports in on different IP subnets and broadcast domains and the target ports also reside in a different IP subnet and broadcast domain. In this case, you should not use port binding.If you configure port binding in this configuration, you may experience these issues:
    • Rescan times take longer than usual.
    • Incorrect number of paths are seen per device.
    • Unable to see any storage from the storage device.

    When to use port binding

    Example




    In this scenario, there are multiple VMkernel ports, all residing in the same IP subnet and broadcast domain. In this case, you must use port binding. If you do not configure port binding in this configuration, you may experience these symptoms:
    • Unable to see storage presented to the ESXi/ESX host.
    • Paths to the storage report as Dead.
    • Loss of path redundancy messages in vCenter Server.
    Note: There have been limitations in the past when using software iSCSI when the iSCSI initiator and target had to be
    on the same subnet. With vSphere 6.5, the software iSCSI initiator and target can be on different subnets. For more information, see What’s New in VMware vSphere 6.5.

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