Storage Multipathing

Storage Multipathing

Dynamic multipathing support is available for Fibre Channel and iSCSI storage backends. By default, XenServer uses round-robin mode load balancing, so both routes have active traffic on them during normal operation. You can enable multipathing in XenCenter or on the xe CLI. For additional information about multipathing, see CTX134881—Configuring Multipathing for XenServer.

Before attempting to enable multipathing, verify that multiple targets are available on your storage server. For example, an iSCSI storage backend queried for sendtargets on a given portal should return 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

To enable storage multipathing using the xe CLI

1. Unplug all PBDs on the host:

xe pbd-unplug uuid=<pbd_uuid>

2. Set the host's other-config:multipathing parameter:

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

3. Set the host's other-config:multipathhandle parameter to dmp:

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

4. 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 re-plug 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 otherconfig: multipathhandle parameter as this will be done automatically.

Multipath support in XenServer is based on the device-mapper multipathd components. Activation and deactivation of multipath nodes is handled automatically by the Storage Manager API. Unlike the standard dmmultipath tools in Linux, device mapper nodes are not automatically created for all LUNs on the system, and it is only when LUNs are actively used by the storage management layer that new device mapper nodes are provisioned. Therefore, it is unnecessary to use any of the dm-multipath CLI tools to query or refresh DM table nodes in XenServer. Should it be 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

MPP RDAC Driver Support for LSI Arrays.

XenServer supports the LSI Multi-Path Proxy Driver (MPP) for the Redundant Disk Array Controller (RDAC) used by Dell MD Series. By default this driver is disabled.

To enable the driver:

1. Open a console on the host, and run the following command:

# /opt/xensource/libexec/mpp-rdac --enable

2. Reboot the host.

To disable the driver:

1. Open a console on the host, and run the following command:

# /opt/xensource/libexec/mpp-rdac --disable

2. Reboot the host.