13.3. Host High Availability

All hosts on the Red Hat Enterprise Virtualization platform work in a cluster mode and therefore need to be fenced by the Manager either automatically or manually. Fencing allows a cluster to react to unexpected host failures as well as enforce power saving, load balancing, and virtual machine availability policies. Therefore, it is highly recommended that you configure the fencing parameters and test their correctness from time to time.
Hosts can be fenced automatically using the power management parameters, or manually by right clicking on a host and using the options on the menu. In a fencing operation, a host is re-booted, and if the host does not return to an active status within a prescribed time, Red Hat Enterprise Virtualization Manager marks it as unresponsive.
If the host is required to run virtual machines that are highly available, power management must be enabled and configured.

13.3.1. Setting the Parameters for Fencing

The parameters for host fencing are set using the Power Management fields on the New Host or Edit Host dialog. Power management enables the system to fence a troublesome host using an additional interface such as a Remote Access Card (RAC).

To set up fencing on a host:

  1. Ensure the Tree tab is selected in the left hand pane of the Administration Portal. Expand the tree view using the + buttons until the host to be fenced is visible. The Hosts tab displays a list of all hosts in the system.
  2. Select the host for which you wish to set up fencing and click the Edit button. The Edit Host dialog displays. Click the Power Management tab.
    Power Management Dialog

    Figure 13.1. Power Management Dialog

    • Enable Power Management: Select this checkbox to turn out-of-band (OOB) power management on. The fields for Power Management are enabled.
    • The Address of the host. This is usually the address of the remote access card (RAC) on the host.
    • A valid User Name for the OOB management.
    • A valid, robust Password for the OOB management.
    • The Type of the fencing device. Select the appropriate device from the drop down list.
      alom Sun Integrated Lights Out Manager (ILOM)
      apc APC Master MasterSwitch network power switch
      bladecenter IBM Bladecentre Remote Supervisor Adapter
      drac5 Dell Remote Access Controller for Dell computers
      eps ePowerSwitch 8M+ network power switch
      ilo HP Integrated Lights Out standard
      ipmilan Intelligent Platform Management Interface
      rsa IBM Remote Supervisor Adaptor
      rsb Fujitsu-Siemens RSB management interface
      wti WTI Network PowerSwitch
      cisco_ucs Cisco UCS Integrated Management Controller


      Depending on the Type selected, some or all of the following fields display on the Power Management tab.
      • Click Secure to use SSH to connect to OOB management.
      • The Port to connect to OOB management.
      • Enter the Slot if a Blade server is being configured.
      • Enter any Options that are needed for the fence-agents commands or ssh command. This is free text field that enables the administrator to enter commands that are not available via the graphical user interface. Red Hat Enterprise Virtualization Manager does not perform any checks on these options. These options should only be used by advanced users, as any errors will cause the host to become unreachable.
    • Click the Test button to test the operation of the OOB management solution. If the power management options can be verified, the text Test Succeeded, Host Status is: on displays.


    Power management parameters (userid, password, options, etc) are tested by Red Hat Enterprise Virtualization Manager only during setup and when required. There are no periodic tests unless manually scheduled. If you choose to ignore alerts about incorrect parameters, or if the parameters are changed on the power management hardware without the corresponding change in Red Hat Enterprise Virtualization Manager, fencing is likely to fail when most needed.
  3. Click OK.
    You are returned to the list of hosts. Note that the exclamation mark next to the host's name has now disappeared, signifying that power management has been successfully configured.