Acquiring DLPAR and CoD resources

In general, PowerHA SystemMirror tries to allocate as many resources as possible to meet the required amount for the application, and uses CoD, if allowed, to do this.

The LPAR node has the LPAR minimum

If the node owns only the minimum amount of resources, PowerHA SystemMirror requests additional resources through DLPAR and CoD.

In general, PowerHA SystemMirror starts counting the extra resources that are required for the application from the minimum amount. That is, the minimum resources are retained for the node's overhead operations, and are not used to host an application.

The LPAR node has enough resources to host an application

The LPAR node that is about to host an application may already contain enough resources (in addition to the LPAR minimum) to meet the required amount of resources for this application.

In this case, PowerHA SystemMirror does not allocate any additional resources and the application can be successfully started on the LPAR node. PowerHA SystemMirror also calculates that the node has enough resources for this application in addition to hosting all other application controllers that could be currently running on the node.

Resources requested from the free pool and from the CoD pool

If the amount of resources in the free pool is insufficient to satisfy the total amount requested for allocation (minimum requirements for one or more applications), PowerHA SystemMirror requests resources from CoD.

If PowerHA SystemMirror meets the requirement for a minimum amount of resources for the application controllers, application controller processing continues. Application controller processing continues even if the total required resources (for one or more applications) have not been met or are only partially met. In general, PowerHA SystemMirror attempts to acquire up to the required amount of resources requested for an application.

If the amount of resources is insufficient to host an application, PowerHA SystemMirror starts resource group recovery actions to move the resource group to another node.

Resources are requested from free pool and from the CoD pool. You can use the Resource allocation order field to specify the order in which the resources are allocated. The resources are released in the reverse order in which they are allocated. The default value for this field is Free pool before Enterprise pool.

The minimum amount requested for an application cannot be satisfied

In some cases, even after PowerHA SystemMirror requests to use resources from the CoD pool, the amount of resources it can allocate is less than the minimum amount specified for an application.

If the amount of resources is still insufficient to host an application, PowerHA SystemMirror starts resource group recovery actions to move the resource group to another node.

The LPAR node is hosting application controllers

In all cases, PowerHA SystemMirror checks whether the node is already hosting application controllers that required application provisioning, and that the LPAR maximum for the node is not exceeded:

• Upon subsequent fallovers, PowerHA SystemMirror checks if the minimum amount of requested resources for yet another application controller plus the amount of resources already allocated to applications residing on the node exceeds the LPAR maximum.
• In this case, PowerHA SystemMirror attempts resource group recovery actions to move the resource group to another LPAR. Note that when you configure the DLPAR and CoD requirements for this application controller, then during cluster verification, PowerHA SystemMirror warns you if the total number of resources requested for all applications exceeds the LPAR maximum.

Allocation of resources in a cluster with multiple applications

If you have multiple applications in different resource groups in the cluster with LPAR nodes, and more than one application is configured to potentially request additional resources through the DLPAR and CoD function, the resource allocation in the cluster becomes more complex.

Based on the resource group processing order, some resource groups (hence the applications) might not be started.