Storage multipathing

Dynamic multipathing support is available for Fibre Channel and iSCSI storage back-ends. You can enable multipathing in XenCenter or on the xe CLI.

Important:

Before attempting to enable multipathing, verify that the following statements are true:

  • Multiple targets are available on your storage server.

    For example, an iSCSI storage back-end queried for sendtargets on a given portal returns multiple targets, as in the following example:

      iscsiadm -m discovery --type sendtargets --portal 192.168.0.161
      192.168.0.161:3260,1 iqn.strawberry:litchie
      192.168.0.204:3260,2 iqn.strawberry:litchie
    
  • For iSCSI only, dom0 has an IP address on each subnet used by the multipathed storage.

    Ensure that for each path you want to have to the storage, you have a NIC and that there is an IP address configured on each NIC. For example, if you want four paths to your storage, you must have four NICs that each have an IP address configured.

  • For HBA only, multiple HBA are connected to the switch fabric.

  1. Open a console on the Citrix Hypervisor server.

  2. Unplug all PBDs on the server by using the following command:

    xe pbd-unplug uuid=<pbd_uuid>
    
  3. Set the value of the other-config:multipathing parameter to true by using the following command:

    xe host-param-set other-config:multipathing=true uuid=<server_uuid>
    
  4. Set the value of the other-config:multipathhandle parameter to dmp by using the following command:

    xe host-param-set other-config:multipathhandle=dmp uuid=<server_uuid>
    
  5. If there are existing SRs on the server running in single path mode but that have multiple paths:

    • Migrate or suspend any running guests with virtual disks in affected the SRs

    • Unplug and replug the PBD of any affected SRs to reconnect them using multipathing:

       xe pbd-unplug uuid=<pbd_uuid>
       xe pbd-plug uuid=<pbd_uuid>
      

To disable multipathing, first unplug your VBDs, set the host other-config:multipathing parameter to false and then replug your PBDs as described above. Do not modify the other-config:multipathhandle parameter as this action is done automatically.

Multipath support in Citrix Hypervisor is based on the device-mapper multipathd components. The Storage Manager API handles activating and deactivating multipath nodes automatically. Unlike the standard dm-multipath tools in Linux, device mapper nodes are not automatically created for all LUNs on the system. Device mapper nodes are only provisioned when LUNs are actively used by the storage management layer. Therefore, it is unnecessary to use any of the dm-multipath CLI tools to query or refresh DM table nodes in Citrix Hypervisor. If it is necessary to query the status of device-mapper tables manually, or list active device mapper multipath nodes on the system, use the mpathutil utility:

mpathutil list
mpathutil status

Notes:

  • Due to incompatibilities with the integrated multipath management architecture, we recommend that you do not use the standard dm-multipath CLI utility with Citrix Hypervisor. Use the mpathutil CLI tool for querying the status of nodes on the host.
  • Multipath support in EqualLogic arrays does not encompass Storage I/O multipathing in the traditional sense of the term. Multipathing must be handled at the network/NIC bond level. For information about configuring network failover for EqualLogic SRs/LVMoISCSI SRs, see the EqualLogic documentation.

Storage multipathing