Microsoft Cluster Server (MSCS) has the ability to define a specific node in the cluster as the preferred node that is to own a particular group. If for any reason this node fails or goes offline, you can set the Cluster service to automatically move these groups back to the node that you want to. This is useful in statically load-balancing the nodes in your cluster. This is referred to as Failover and Failback policies.
Setting Failover PolicyTo set the Failover policy for a group, use the Failover tab for the group. You can set the failover threshold and the failover period. The failover threshold is the number of times the group can fail over within the number of hours specified by the failover period. For example, if a group failover threshold is set to 5, and its failover period set to 3, Cluster Server will failover the group at most five times within a three hour period. The next time a resource in the group exceeds its failure threshold count, Cluster Server will leave the resource in the offline state instead of failing over the group.
NOTE: A group itself does not fail. Only when the following conditions are met for a resource within the group, will the group attempt a failover thus incrementing the Group's failover count.
- The number of failures for a specific resource has exceeded its threshold count within the defined period.
- The resource is defined to "Affect the group".
Setting Failback PolicyBy default, groups are set not to failback. Unless you manually configure your group to failback after failover, it continues to run on the alternate node after the failed node comes back online.
When you configure a group to automatically failback to the preferred node, you specify whether you want the group to failback as soon as the preferred node is available or to failback only during specific hours that you define. This option is useful if you want the failback to occur after peak business hours, or if you want to make sure the preferred node is able to support the group when it does come back online.
When setting the "Allow failback", you have two options, Immediate and Failback Between. When setting it to Immediately, ailback will occur as soon as the Cluster Service detects that the preferred owner is now online. When setting the Failback Between, it is hours on a 24 hour clock (i.e. 1 is 1:00am, 15 is 3:00pm, etc). So if you were to set this to Failback between 1 and 2, it means between 1:00am and 2:00am. This is used to prevent interruption of the availability of the cluster resources in that group during peak hours.If you were to set this to between 1 and 1, it means the current 24-hours and is the same setting as Immediate.
The group must be configured to have a preferred owner to failback. You can specify a preferred owner on the General tab of the group Properties dialog box.
NOTE: The "Preferred Owner" of a group must be specified for failback to occur. The preferred owner is the node that one configures to (under normal operating circumstances) to host the group. Furthermore, on a resource level, the resource must be configured to have both nodes as "Possible Owners" for the resource to failover.
Testing Failover PolicesYou can test the failover policies you establish for a single group and its resources by manually failing over those elements.
To test the failover policy for a group, type 0 (zero) for the Threshold in the Properties dialog box for a specific resource. Then, right-click on that resource and click Initiate Failure. Cluster Server immediately fails over the group to the alternate node.
In a test environment, you can fail over all groups from one node to another by using Cluster Administrator to stop the Cluster Server, pressing the reset button on the computer, or turning off the power to one of the nodes.
NOTE: Removing the shared SCSI/Fibre cable between either node and the shared disk array is not a valid failover test. The cluster service must have access to the shared array at all times for failover to succeed.
Article ID: 197047 - Last Review: Sep 11, 2011 - Revision: 1
Microsoft Windows 2000 Advanced Server, Microsoft Windows NT Server 4.0 Enterprise Edition