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3.4. Global Cluster Properties

When you select a cluster to configure, a cluster-specific page is displayed. The page provides an interface for configuring cluster-wide properties. You can configure cluster-wide properties by clicking on Configure along the top of the cluster display. This yields a tabbed interface which provides the following tabs: General Properties, Fence Daemon Properties, Network Configuration, and QDisk Configuration. To configure the parameters in those tabs, follow the steps in this section. If you do not need to configure parameters in a tab, skip the step for that tab.
  1. General Properties tab — This tab displays the cluster name and provides an interface for modifying the configuration version.
    • The Cluster Name text box displays the cluster name; it does not accept a cluster name change. The only way to change the name of a cluster is to create a new cluster configuration with the new name.
    • The Configuration Version value is set to 1 by default and is automatically incremented each time you modify your cluster configuration. However, if you need to set it to another value, you can specify it at the Configuration Version text box.
    If you have changed the Configuration Version value, click Apply for this change to take effect.
  2. Fence Daemon Properties tab — This tab provides an interface for configuring these Fence Daemon Properties parameters: Post-Fail Delay and Post-Join Delay. The values you configure for these parameters are general fencing properties for the cluster. To configure specific fence devices for the nodes of the cluster, use the Fence Devices menu item of the cluster display, as described in Section 3.5, “Configuring Fence Devices”.
    The general fencing properties for the cluster you can configure with the Fence Daemon Properties tab are summarized as follows:
    • The Post-Fail Delay parameter is the number of seconds the fence daemon (fenced) waits before fencing a node (a member of the fence domain) after the node has failed. The Post-Fail Delay default value is 0. Its value may be varied to suit cluster and network performance.
    • The Post-Join Delay parameter is the number of seconds the fence daemon (fenced) waits before fencing a node after the node joins the fence domain. The Post-Join Delay default value is 3. A typical setting for Post-Join Delay is between 20 and 30 seconds, but can vary according to cluster and network performance.
    Enter the values required and click Apply for changes to take effect.

    Note

    For more information about Post-Join Delay and Post-Fail Delay, refer to the fenced(8) man page.
  3. Network Configuration tab — This tab provides an interface for configuring multicast parameters.
    You can use this tab to configure these multicast parameters: Let cluster choose the multicast address and Specify the multicast address manually. The default setting is Let cluster choose the multicast address. If you need to use a specific multicast address, click Specify the multicast address manually and enter a multicast address into the text box.
    You can enter advanced cluster properties by clicking Show Advanced Properties, which reveals a list of advanced properties you can reset from their default values. It is recommended that you leave these properties at their default values.
    Click Apply for changes to take effect.
    If you do not specify a multicast address, the Red Hat High Availability Add-On software creates one based on the cluster ID. It generates the lower 16 bits of the address and appends them to the upper portion of the address according to whether the IP protocol is IPV4 or IPV6:
    • For IPV4 — The address formed is 239.192. plus the lower 16 bits generated by Red Hat High Availability Add-On software.
    • For IPV6 — The address formed is FF15:: plus the lower 16 bits generated by Red Hat High Availability Add-On software.
    If you do not specify a multicast address, the Red Hat High Availability Add-On software creates one by generating the lower 16 bits of the address and appending them to the upper portion of the address, 239.192. To ensure a unique multicast address, the Red Hat High Availability Add-On software generates the lower 16 bits based on the cluster ID.

    Note

    The cluster ID is a unique identifier that cman generates for each cluster. To view the cluster ID, run the cman_tool status command on a cluster node.
    If you do specify a multicast address, you should use the 239.192.x.x series (or FF15:: for IPv6) that cman uses. Otherwise, using a multicast address outside that range may cause unpredictable results. For example, using 224.0.0.x (which is "All hosts on the network") may not be routed correctly, or even routed at all by some hardware.

    Note

    If you specify a multicast address, make sure that you check the configuration of routers that cluster packets pass through. Some routers may take a long time to learn addresses, seriously impacting cluster performance.
  4. QDisk Configuration tab — This tab provides an interface for configuring these Quorum Disk Configuration parameters: Do not use a Quorum Disk, Use a Quorum Disk, Interval, Votes, TKO, and Minimum Score. This tab also provides an interface to specify a physical device to use, and to specify the heuristics to use. The Do not use a Quorum Disk parameter is enabled by default. Table 3.1, “Quorum-Disk Parameters” describes the parameters. If you need to use a quorum disk, click Use a Quorum Disk, enter quorum disk parameters, click Apply, and restart the cluster for the changes to take effect.

    Important

    Quorum-disk parameters and heuristics depend on the site environment and the special requirements needed. To understand the use of quorum-disk parameters and heuristics, refer to the qdisk(5) man page. If you require assistance understanding and using quorum disk, contact an authorized Red Hat support representative.

    Note

    Clicking Apply on the QDisk Configuration tab propagates changes to the cluster configuration file (/etc/cluster/cluster.conf) in each cluster node. However, for the quorum disk to operate, you must restart the cluster (refer to Section 4.3, “Starting, Stopping, Restarting, and Deleting Clusters”).
Table 3.1. Quorum-Disk Parameters
Parameter Description
Do not use a Quorum Disk Disables quorum disk. Disables quorum-disk parameters in the Qdisk Configuration tab.
Use a Quorum Disk Enables quorum disk. Enables quorum-disk parameters in the Qdisk Configuration tab.
Interval The frequency of read/write cycles, in seconds. The value of Interval is automatically determined if left blank in the Quorum Disk Configuration dialog box.
Votes The number of votes the quorum daemon advertises to cman when it has a high enough score. The value of Votes is automatically determined if left blank in the Quorum Disk Configuration dialog box.
TKO The number of cycles a node must miss to be declared dead. The value of TKO is automatically determined if left blank in the Quorum Disk Configuration dialog box.
Minimum Score The minimum score for a node to be considered "alive". If omitted or set to 0, the default function, floor((n+1)/2), is used, where n is the sum of the heuristics scores. The Minimum Score value must never exceed the sum of the heuristic scores; otherwise, the quorum disk cannot be available.
Specify physical device: By device label Specifies the quorum disk label created by the mkqdisk utility. If this field is used, the quorum daemon reads the /proc/partitions and checks for qdisk signatures on every block device found, comparing the label against the specified label. This is useful in configurations where the quorum device name differs among nodes.
Device The storage device the quorum daemon uses. The device must be the same on all nodes.
Label Specifies the quorum disk label created by the mkqdisk utility. If this field contains an entry, the label overrides the Device field. If this field is used, the quorum daemon reads /proc/partitions and checks for qdisk signatures on every block device found, comparing the label against the specified label. This is useful in configurations where the quorum device name differs among nodes.
Heuristics
Path to Program — The program used to determine if this heuristic is available. This can be anything that can be executed by /bin/sh -c. A return value of 0 indicates success; anything else indicates failure. This field is required.
Interval — The frequency (in seconds) at which the heuristic is polled. The default interval for every heuristic is 2 seconds.
Score — The weight of this heuristic. Be careful when determining scores for heuristics. The default score for each heuristic is 1.
TKO — The number of consecutive failures required before this heuristic is declared unavailable.
Apply Propagates the changes to the cluster configuration file (/etc/cluster/cluster.conf) in each cluster node.