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Resource Optimized High Availability PowerHA System Mirror 7.2

Many PowerHA implementations include the planned use of Capacity on Demand (CoD) or Power Enterprise Pool mobile activations on the failover server. Prior versions of PowerHA required you to manually script the activation/use of these resources. PowerHA SystemMirror version 7.2 includes a new automate resource activation feature called Resource Optimized High Availability (ROHA). ROHA automates the activation of On/Off CoD resources or the reassignment of mobile activations during an active failover. ROHA then assigns these resources to the PowerHA failover LPAR.

ROHA highlights

PowerHA failover LPARs are often configured with minimal resources when they are operating in standby mode. When a failover event occurs, additional processor core and memory resources are assigned to the failover LPAR, bringing it up to the size necessary to run the workload. Prior to ROHA, scripts had to be created for resource activation and assignment to the failover LPAR. ROHA automation will work any combination of the following resources:

  • Existing activated/unallocated resources
  • Power Enterprise Pool mobile activations, referred to as Enterprise Pool CoD (EPCoD)
  • Unactivated CoD resources

During the ROHA configuration process you can specify whether you want to use EPCoD or On/Off activations with ROHA.

Getting Started with ROHA

When setting up PowerHA resources groups, one of the resources included is an application controller. Applications controllers have:

  • A name for the application controller
  • Event definition scripts used to start and stop the applications
  • One or more event monitor definitions

When including ROHA in your PowerHA design, you must create hardware provisioning information for each application controller. ROHA can provision from the three categories of hardware resources described above. You have the option to choose which of these resource categories you want to make available to ROHA. EPCoD resources are a great fit for use with ROHA. During an activate failover, mobile activations will be moved from the primary server to the failover server. This eliminates the need to have idle activated/unallocated resources on the failover server or to enable the use of On/Off CoD. On/Off CoD activations incur usage charges that are measured in 24-hour increments. The first time your provision resources, the HMC will prompt you to regarding permission to use On/Off activations by ROHA. This helps eliminate undesired charges for unintended use of On/Off CoD resources.

ROHA in action

As previously mentioned, ROHA has three sources for obtaining resources to assign to a failover LPAR during an active PowerHA event. ROHA prioritizes the use of these resources in the following order:

  1. Existing activated/unallocated resources that can be directly assigned to the failover LPAR using Dynamic LPAR (DLPAR) operations
  2. EPCoD mobile resources that can be transferred to the server hosting the failover LPAR. Transferred mobile activations appear on the failover server as activated/unallocated. DLPAR operations are then used to assign the resources to the failover LPAR.
  3. On/Off CoD resources, which also appear in the activated/unallocated pool after activation. DLPAR operations complete their assignment to the failover LPAR.

ROHA automates all of this activity and will only activate the resources types you have enabled for use.

ROHA resource planning

Prior to configuring ROHA, you will need to gather information about your PowerHA cluster environment(s). This includes:

  • List of all participating PowerHA LPARs
  • PowerHA LPAR resource requirements (cores, virtual processors and memory)
  • The HMC(s) used to mange each of these LPARs
  • Details on available resources that will be available to ROHA:
    • Active/Unallocated
    • EPCoD
    • CoD

You must also consider any planned use of these resources by other LPARs running on the servers. Examples of non-PowerHA use include Live Partition Mobility (LPM) and end-of-month peak processing.

You can manually enter ROHA configuration commands or use the Systems Management Interface Tool (SMIT). The following command can be used to check the status of the ROHA configuration: # clmgr view report roha.

Highlights from this command’s output include:

  • Adjust shared processor pool size if needed (yes/no)
  • Force release of DLPAR resources from other LPARs (yes/no)
  • Permission to activate CoD resources (yes/no)
  • EPCoD available? (yes/no)
  • Status of available (available unallocated) EPCoD resources

This information can be used to confirm the ROHA configuration aligns with the required failover LPAR resources allocations for a PowerHA failover event.

Preparing the HMC to work with ROHA

All LPARs that are configured with ROHA must have SSH communication enabled between the LPAR and the HMC(s). The SSH configuration cannot have a required password and should be configured to use a public/private key pair.

It’s typical to have dual HMCs configured, especially for servers with PowerHA cluster. These are defined to ROHA in a list. All HMC-to-LPAR communications will use the first HMC in the list. If communications with that HMC are unsuccessful, the next HMC in the list will be utilized. When servers are configured with EPCoD, EPCoD configuration rules require the HMCs to be designated as master and backup. The master HMC must be used for all EPCoD mobile activation assignments. If it is not accessible, you would normally log into the backup HMC and run a command to make it the master HMC. With ROHA, if the primary HMC becomes unavailable, ROHA automatically enables master mode on the backup HMC.

PowerHA 7.2 support details

PowerHA System mirror 7.2 is available in both Standard and Enterprise versions. PowerHA 7.2 is supported on POWER6 and newer servers. It requires AIX 6.1 TL09, AIX 7.1 TL03 or higher.

Enhance your PowerHA environment

The new Resource Optimized High Availability feature of PowerHA 7.2 simplifies PowerHA configuration and scripting. The process of implementing ROHA also brings more structure to planning for the allocation of resources during both normal operation and active failover operation environments. When planning for the use of ROHA, you should also consider the use of processor core and memory resources by other LPARs running on the same servers.

Charlie Cler supports customers in a solutions-architect role at Forsythe Technology Inc. He can be reached at ccler@forsythe.com.

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