Planning for PowerHA SystemMirror for Linux

All the relevant Red Hat Package Manager (RPM) are installed automatically on starting the PowerHA® SystemMirror® installation script.

When a node is configured with multiple connections to a single network, the network interfaces serve different functions in the PowerHA SystemMirror.

A service interface is a network interface that is configured with the PowerHA SystemMirror service IP label. The service IP label is used by clients to access application programs. The service IP is only available when the corresponding resource group is online.

A persistent node IP label is an IP alias that can be assigned to a specific node on a cluster network. A persistent node IP label always stays on the same node (node-bound), and coexists on an NIC that already has a service or boot IP label defined. A persistent node IP label does not require installing an extra physical NIC on that node.

If you assign a persistent node IP label, it provides a node-bound address that you can use for administrative purposes because a connection to a persistent node IP label always goes to a specific node in the cluster. You can have one persistent node IP label per node.

For PowerHA SystemMirror, you must configure a persistent IP label for each cluster node. This is useful to access a particular node in a PowerHA SystemMirror cluster for running reports or for diagnostics. This provides advantage that the PowerHA SystemMirror can access the persistent IP label on the node despite individual NIC failures, provided spare NICs are present on the network.

If you assign IP aliases to NICs, it allows you to create more than one IP label on the same network interface. During an IP address takeover by using the IP aliases, when an IP label moves from one NIC to another, the target NIC receives the new IP label as an IP alias and keeps the original IP label and hardware address.

Configuring networks for IP address takeover (IPAT) by using IP aliases simplifies the network configuration in the PowerHA SystemMirror. You can configure a service address and one or more boot addresses for NICs.

PowerHA SystemMirror uses a technology referred to as IPAT by using IP aliases for keeping IP addresses highly available.

During a node fallover event, the service IP label that is moved is placed as an alias on the NIC of target node in addition to any other service labels configured on that NIC.

If your environment has multiple adapters on the same subnet, all the adapters must have the same network configuration and the adapters must be part of the PowerHA SystemMirror configuration.