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 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

Unplug all PBDs on the host:

xe pbd-unplug uuid=pbd_uuid

Set the host’s other-config:multipathing parameter:

xe host-param-set other-config:multipathing=true uuid=host_uuid

Set the host’s other-config:multipathhandle parameter to dmp:

xe host-param-set other-config:multipathhandle=dmp uuid=host_uuid

If there are existing SRs on the host 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-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 XenServer 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 XenServer. 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 XenServer. 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

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