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The PowerHA SystemMirror software supports up to four nodes in a cluster. Figure 11-2 shows that each node is identified by a unique name. In PowerHA SystemMirror, a node name and a host name must be the same, and each node is identified by a unique name. In PowerHA SystemMirror, the nodes can be Bare Metal or virtual machines (VMs). 

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The topology of PowerHA SystemMirror for Linux is similar to AIX to ensure that applications and its resources are kept highly available. Some of those resources are: 

GLYPH<SM590000> Service IP labels or addresses 

GLYPH<SM590000> Physical disks 

GLYPH<SM590000> Volume groups (VGs) 

GLYPH<SM590000> Logical volumes 

GLYPH<SM590000> File systems 

GLYPH<SM590000> Network File System (NFS) 

## 11.1.2 Differences between PowerHA SystemMirror for AIX and Linux 

Although the topology and architecture of PowerHA SystemMirror for AIX and Linux are similar, there are some differences that are highlighted in this section. 

## Cluster configuration changes 

The changes applied to the cluster configuration by the user are immediately applied to all nodes without a manual synchronization procedure, unlike in PowerHA SystemMirror for AIX. 

## Split policy 

As in AIX, PowerHA for Linux split events occur when a group of nodes in a cluster cannot communicate with each other, so the event splits the cluster into two or more partitions. Afterward, in PowerHA for Linux manual intervention is required. 

## Split policy: Manual 

If the split policy is set to manual and the event happens, a verification process and manual intervention is required. You find that PENDING_QUORUM  ran the lssrc -ls IBM.RecoveryRM |grep "Opera-tional Quorum State  command, which indicates that a split operation occurred and manual intervention is needed. For the survivor node to take over the failed resources, run the runact  command. 

