In a SAIN system, nodes have both physical and logical connections to the SAN storage. The physical connections are through paths established by Fibre Channel cables and, in some systems, Fibre Channel switches. The logical connections are through mappings of the logical volumes in the storage array to the nodes.
In an HCP SAIN system, each node has two physical paths to the storage array. This is called multipathing.
The following figure shows two nodes, A and B, at the bottom, each with a multipath connection to the storage array at the top.
To support zero-copy failover, the logical volumes in the storage array must be cross-mapped to the nodes. Cross-mapping means that each logical volume that maps to one node (A) must also map to the same second node (B), called the peer node. The mappings to node A are the primary mappings for those logical volumes, and the mappings to node B are the standby mappings. Similarly, each logical volume with a primary mapping to node B must have a standby mapping to node A.
The following figure shows two sets of logical volumes in a storage array that map to two nodes, A and B. The primary mappings for each node are shown in blue. The secondary mappings are shown in red.