Planning parallel or serial order for processing resource groups

The following processes are completed during acquisition:

1. PowerHA SystemMirror acquires the resource groups serially in the order that you specified in the list.
2. PowerHA SystemMirror acquires the remaining resource groups in parallel.

During the release of resource groups, the process is reversed:

1. PowerHA SystemMirror releases the resource groups for which you did not define a specific serial order in parallel.
2. The remaining resource groups in the cluster are processed in the order that you specified for these resource groups in the list.
3. If you upgraded your cluster from a previous version of PowerHA SystemMirror, for more information about which processing order is used in this case, see Upgrading a PowerHA SystemMirror cluster.
   Note: Even if you specify the order of resource group processing on a single node, the actual fallover of the resource groups may be triggered by different policies. Therefore, it is not guaranteed that resource groups are processed cluster-wide in the order specified because the serial customized processing order of resource groups applies to their processing on a particular node only.
4. When resource groups are processed in parallel, fewer cluster events occur in the cluster. In particular, events such as node_up_local or get_disk_vg_fs do not occur if resource groups are processed in parallel.
5. As a result, using parallel processing reduces the number of particular cluster events for which you can create customized pre-event or post-event scripts. If you start using parallel processing for some of the resource groups in your configuration, be aware that your existing pre-event or post-event scripts might not work for these resource groups.
6. Parallel and serial processing of resource groups is reflected in the event summaries in the hacmp.out file.

   For more information about how to configure customized serial acquisition and release order of resource groups, see Configuring processing order for resource groups.

Dependent resource groups and parallel or serial order

Although by default PowerHA SystemMirror processes resource groups in parallel, if you establish dependencies between some of the resource groups in the cluster, processing may take longer than it does for clusters without dependent resource groups as there may be more processing to do to handle one or more rg_move events

Upon acquisition, first the parent or higher priority resource groups are acquired, then the child resource groups are acquired. Upon release, the order is reversed. The remaining resource groups in the cluster (those that do not have dependencies themselves) are processed in parallel.

Also, if you specify serial order or processing and have dependent resource groups configured, make sure that the serial order does not contradict the dependency specified. The resource groups dependency overrides any serial order in the cluster.