PowerHA SystemMirror integration with the CoD function

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By integrating with DLPAR and CoD, PowerHA® SystemMirror® ensures that each node can support the application with reasonable performance at a minimum cost. You can use the On/Off CoD function to upgrade the capacity of the logical partition when your application requires more resources, without having to pay for idle capacity until you need it. You can use Enterprise Pool CoD (EPCoD) to share resources across systems in the same mirror pool.

You can configure cluster resources so that the logical partition with minimally allocated resources serves as a standby node, and the application resides on another LPAR node that has more resources than the standby node. This way, you do not use any additional resources that the frames have until the resources are required by the application.

When it is necessary to run the application on the standby node, PowerHA SystemMirror ensures that the node has sufficient resources to successfully run the application. The resources can be dynamically allocated from the free pool. The DLPAR function provides the resources to the standby node, by allocating the resources that are available in the free pool on the system.

If there are not enough available resources in the free pool that can be allocated through DLPAR to the standby node, PowerHA SystemMirror can dynamically provision resources from the EPCoD resource pool or the On/Off resource pool. When the free pool contains enough resources, these resources are allocated by PowerHA SystemMirror through a DLPAR operation for the standby node.

The On/Off CoD resources are temporary resources that you pay for on a per consumption basis. EPCoD resources are permanent resources that are a onetime payment and has unlimited use. To reduce costs, PowerHA SystemMirror always gets resources from the EPCoD resource pool before getting resources from the On/Off resource pool. PowerHA SystemMirror always releases resources to the On/Off resource pool before releasing resources to the EPCoD resource pool.

The following table displays all available types of CoD for PowerHA SystemMirror.

CoD type	PowerHA SystemMirror Version 7.1	PowerHA SystemMirror Version 7.2
On/Off CoD	CPU: Yes Memory: No	CPU: Yes Memory: Yes
Trial CoD	Yes	Yes
Enterprise Pool CoD	No	Yes

You can configure a PowerHA SystemMirror cluster within one or more IBM® Power Systems™ servers, using two or more logical partitions. You can also configure a cluster on a subset of LPARs within one frame. Or, the cluster can use partitions from two or more frames, where the nodes can be defined as a subset of LPARs from one frame and a subset of LPARs from another frame, all connected to one or more HMCs. The following figure illustrates a typical two-frame configuration:

Figure 1. PowerHA SystemMirror cluster configuration with LPARs

Terminology for resource types and memory allocation

The following terms can help you to distinguish between different types of resources allocation that can occur in a PowerHA SystemMirror cluster that uses DLPAR and CoD functions:

Installed amount of resources: The number of CPUs and the amount of memory that is physically present on the frame. Although these resources are physically present, they are only usable if they are configurable resources.
Configurable amount of resources: The number of CPUs and the amount of memory that is physically available for use by all LPARs on the frame. This amount includes all permanent resources, paid for resources, and CoD resources that are active on the frame (On/Off or EPCoD).
Inactive amount of resources: The difference between the installed amount of resources and the configurable amount of resources. Also called unlicensed resources. You must have an inactive amount of resources to be able to use CoD resources.
Free pool amount of resources: The number of CPUs and the amount of memory that can be dynamically allocated by PowerHA SystemMirror through the HMC to an LPAR that requires more resources. The free pool amount of resources is the difference between the configurable amount of resources on the frame minus the resources that are current being used by the LPAR.
The free pool includes resources on a particular frame only. For example, if a cluster is configured with LPARs that reside on frames A and B, PowerHA SystemMirror does not request resources from a free pool on frame B for an LPAR that resides on frame A.
Enterprise Pool CoD (EPCoD) amount of resources: The number of CPUs and the amount of memory that is available in the EPCoD resource pool that can be allocated by PowerHA SystemMirror if the frame requires more resources. When EPCoD resources are allocated to a frame, the amount of configurable resources on the frame is increased. The increase of configurable resources makes it possible for a DLPAR operation to provide more resources to an LPAR.
You can use the lscodpool command on the HMC to view the characteristics on the EPCoD resource pool. You can also use the clmgr view report roha command on a PowerHA SystemMirror node to view general information that is related to the Resource Optimized High Availability (ROHA) data.
Note: The EPCoD resource pool includes resources for multiple frames.
On/Off CoD amount of resources: The number of CPUs and the amount of memory that is available in the On/Off resource pool that can be allocated by PowerHA SystemMirror if the frame requires more resources. When On/Off CoD resources are allocated to a frame, the amount of configurable resources on the frame is increased. The increase of configurable resources makes it possible for a DLPAR operation to provide more resources to an LPAR.
You can use the lscod command on the HMC to view the characteristics on the On/Off CoD resource pool. You can also use the clmgr view report roha command on a PowerHA SystemMirror node to view general information that is related to the ROHA data.
Note: The On/Off CoD resource pool includes resources for a single frame.
LPAR minimum amount: The minimum amount (or quantity) of a resource, such as CPU or memory, that an LPAR requires to be brought online or started. The LPAR does not start unless it meets the specified LPAR minimum. When DLPAR operations are performed between LPARs, the amount of resources that are removed from an LPAR cannot go less than this value. This value is set on the HMC on the LPAR profile and is not modified by PowerHA SystemMirror. All allocations that are performed by PowerHA SystemMirror are computed starting for this minimum value.
LPAR desired amount: The desired amount of a resource that an LPAR acquires when it starts, if the resources are available. This value is set on the HMC on the LPAR profile and is not modified by PowerHA SystemMirror.
LPAR maximum amount: The maximum amount (or quantity) of a resource that an LPAR can acquire. When DLPAR operations are performed, the amount of resources added to an LPAR cannot go more than this value. This value is set on the HMC on the LPAR profile and is not modified by PowerHA SystemMirror. Use the lshwres command on the HMC to verify the minimal, desired, and maximum values. You can also use the clmgr view report roha command on a PowerHA SystemMirror node to view general information that is related to the ROHA data.