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Managing Serviceguard Fifteenth Edition > Chapter 4 Planning and Documenting an HA Cluster

Cluster Lock Planning


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The purpose of the cluster lock is to ensure that only one new cluster is formed in the event that exactly half of the previously clustered nodes try to form a new cluster. It is critical that only one new cluster is formed and that it alone has access to the disks specified in its packages. You can specify an LVM lock disk, a lock LUN, or a quorum server as the cluster lock. For more information about the cluster lock, and requirements and recommendations, see “Cluster Lock”.

NOTE: You cannot use more than one type of lock in the same cluster.

A one-node cluster does not require a lock. Two-node clusters require the use of a cluster lock, and a lock is recommended for larger clusters as well. Clusters larger than four nodes can use only a quorum server as the cluster lock. In selecting a cluster lock configuration, be careful to anticipate any potential need for additional cluster nodes.

For more information on lock disks, lock LUNs, and the Quorum Server, see “Choosing Cluster Lock Disks”, “Setting Up a Lock LUN”, and “Setting Up and Running the Quorum Server”.

Cluster Lock Disk and Re-formation Time

cmquerycl displays the failover time for the cluster in the Possible Cluster Lock Devices section, for example:

Possible Cluster Lock Devices:/dev/dsk/c0t1d4 30 secondsNote: all lock disks have the same failover time

All disks in all volume groups which are accessible by all nodes in the cluster are potential cluster lock devices, but because it takes a fixed amount of time to acquire the cluster lock, regardless of the lock device, only the first potential lock device is displayed. You may need to choose a different device because of power considerations; see “Power Supply Planning ”.

Planning for Expansion

Bear in mind that a cluster with more than 4 nodes cannot use a lock disk or lock LUN. Thus, if you plan to add enough nodes to bring the total to more than 4, you should use a quorum server.

Using a Quorum Server

The operation of Quorum Server is described under “Use of the Quorum Server as the Cluster Lock”. See also “Cluster Lock”.

A quorum server:

  • Can be used with up to 150 clusters, not exceeding 300 nodes total.

  • Can support a cluster with any supported number of nodes.

  • Must be configured on an IPv4, not an IPv6, network.

  • Can communicate with the cluster on up to two subnets (a primary and an alternate).

The HP Serviceguard Quorum Server Version A.03.00 Release Notes provide detailed information on installing, updating, configuring and running the Quorum Server are ed

IMPORTANT: If you plan to use a Quorum Server, make sure you read the HP Serviceguard Quorum Server Version A.03.00 Release Notes before you proceed. You can find them at: http://www.docs.hp.com -> High Availability -> Quorum Server. You should also consult the Quorum Server white papers at the same location.

Quorum Server Worksheet

You may find it useful to use the Quorum Server Worksheet that follows to identify a quorum server for use with one or more clusters. You may also want to enter quorum server host and timing parameters on the Cluster Configuration Worksheet. Blank worksheets are in Appendix F “Blank Planning Worksheets”.

On the QS worksheet, enter the following:

Quorum Server Host

Enter the host name (and alternate address, if any) for the quorum server.

IP Address

Enter the IP v4 address(es) by which the quorum server will be connected to the cluster.

Supported Node Names

Enter the name (39 characters or fewer) of each cluster node that will be supported by this quorum server. These entries will be entered into qs_authfile on the system that is running the quorum server process.

    Quorum Server Data:

    QS Hostname: __________IP Address: _______________IP Address:_______________


    Quorum Services are Provided for:

Cluster Name: ___________________________________________________________

    Host Names ____________________________________________

    Host Names ____________________________________________

Cluster Name: ___________________________________________________________

    Host Names ____________________________________________

    Host Names ____________________________________________

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