External storage system zones

Ensure that you are familiar with the external storage system zoning details. Switch zones that contain storage system ports must not have more than 40 ports. A configuration that exceeds 40 ports is not supported.

Zones

The switch fabric must be zoned so that the nodes can detect the back-end storage systems and the front-end host HBAs. Typically, the front-end host HBAs and the back-end storage systems are not in the same zone. The exception to this is where split host and split storage system configuration is in use.

All nodes in a system must be able to detect the same ports on each back-end storage system. Operation in a mode where two nodes detect a different set of ports on the same storage system is degraded, and the system logs errors that request a repair action. This can occur if inappropriate zoning is applied to the fabric or if inappropriate LUN masking is used. This rule has important implications for back-end storage, such as IBM® DS4000 storage systems, which impose exclusive rules for mappings between HBA worldwide node names (WWNNs) and storage partitions.

Each port must be zoned so that it can be used for internode communications. When configuring switch zoning, you can zone some node ports to a host or to back-end storage systems.

When configuring zones for communication between nodes in the same system, the minimum configuration requires that all Fibre Channel ports on a node detect at least one Fibre Channel port on each other node in the same system. You cannot reduce the configuration in this environment.

It is critical that you configure storage systems and the SAN so that a system cannot access logical units (LUs) that a host or another system can also access. You can achieve this configuration with storage system logical unit number (LUN) mapping and masking.

If a node can detect a storage system through multiple paths, use zoning to restrict communication to those paths that do not travel over ISLs.

However, to accommodate the limitations of some switch vendors on the number of ports or worldwide node names (WWNNs) that are allowed in a zone, you can further reduce the number of ports or WWNNs in a zone. Such a reduction can result in reduced redundancy and additional workload being placed on other system nodes and the Fibre Channel links between the nodes of a system.

If the round-trip latency between systems is greater than 80 milliseconds, stricter configuration requirements apply:
  • Use SAN zoning and port masking to ensure that two Fibre Channel ports on each node that is used for replication are dedicated for replication traffic.
  • Apply SAN zoning to provide separate intersystem zones for each local-to-remote I/O group pair that is used for replication.

The minimum configuration requirement is to zone both nodes in one I/O group to both nodes in one I/O group at the secondary site. The I/O group maintains fault tolerance of a node or port failure at either the local or remote site location. It does not matter which I/O groups at either site are zoned because I/O traffic can be routed through other nodes to get to the destination. However, if an I/O group that is doing the routing contains the nodes that are servicing the host I/O, there is no additional burden or latency for those I/O groups because the I/O group nodes are directly connected to the remote system.