Zoning guidelines

Ensure that you are familiar with the zoning guidelines for storage system zones and host zones.

Paths to hosts

The number of paths through the network from the SAN Volume Controller nodes to a host must not exceed eight. Configurations in which this number is exceeded are not supported.

Each node has four ports and each I/O group has two nodes. Therefore, without any zoning, the number of paths to a VDisk would be eight multiplied by the number of host ports.
This rule exists to limit the number of paths that must be resolved by the multipathing device driver.

If you want to restrict the number of paths to a host, zone the switches so that each host bus adapter (HBA) port is zoned with one SAN Volume Controller port for each node in the cluster. If a host has multiple HBA ports, zone each port to a different set of SAN Volume Controller ports to maximize performance and redundancy.

Storage system zones

Switch zones that contain storage system ports must not have more than 40 ports. A configuration that exceeds 40 ports is not supported.

SAN Volume Controller zones

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

When configuring zones for communication between nodes in the same cluster, 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 cluster. You cannot reduce the configuration in this environment.

It is critical that you configure storage systems and the SAN so that a cluster cannot access logical units (LUs) that a host or another cluster 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.

With Metro Mirror and Global Mirror configurations, additional zones are required that contain only the local nodes and the remote nodes. It is valid for the local hosts to see the remote nodes or for the remote hosts to see the local nodes. Any zone that contains the local and the remote back-end storage systems and local nodes or remote nodes, or both, is not valid.

For clusters that are running SAN Volume Controller version 5.1, configure your system so that all fibre-channel node ports detect at least one fibre-channel port on each node in the remote cluster. For best results in Metro Mirror and Global Mirror configurations, zone each node so that it can communicate with at least one fibre-channel port on each node in each remote cluster. This configuration maintains redundancy of the fault tolerance of port and node failures within local and remote clusters. For communications between multiple SAN Volume Controller version 5.1 clusters, this also achieves optimal performance from the nodes and the intercluster links.

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 cluster nodes and the fibre-channel links between the nodes of a cluster.

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 cluster.

For clusters that are running SAN Volume Controller version 4.3.1 or earlier, the minimum configuration requirement is that all nodes must detect at least one fibre-channel port on each node in the remote cluster. You cannot reduce the configuration in this environment.

In configurations with a version 5.1 cluster that is partnered with a cluster that is running a SAN Volume Controller version 4.3.1 or earlier, the minimum configuration requirements of the version 4.3.1 or earlier cluster apply.

If only a subset of the I/O groups within a cluster are using Metro Mirror and Global Mirror, you can restrict the zoning so that only those nodes can communicate with nodes in remote clusters. You can have nodes that are not members of any cluster zoned to detect all of the clusters. You can then add a node to the cluster in the event that you must replace a node.

Host zones

The configuration rules for host zones are different depending upon the number of hosts that will access the cluster. For configurations of less than 64 hosts per cluster, the SAN Volume Controller supports a simple set of zoning rules that enable a small set of host zones to be created for different environments. For configurations of more than 64 hosts per cluster, the SAN Volume Controller supports a more restrictive set of host zoning rules.

Zoning that contains host HBAs must ensure host HBAs in dissimilar hosts or dissimilar HBAs are in separate zones. Dissimilar hosts means that the hosts are running different operating systems or are different hardware platforms; thus different levels of the same operating system are regarded as similar.

To obtain the best overall performance of the system and to prevent overloading, the workload to each SAN Volume Controller port must be equal. This can typically involve zoning approximately the same number of host fibre-channel ports to each SAN Volume Controller fibre-channel port.

Clusters with less than 64 hosts

For clusters with less than 64 hosts attached, zones that contain host HBAs must contain no more than 40 initiators including the SAN Volume Controller ports that act as initiators. A configuration that exceeds 40 initiators is not supported. A valid zone can be 32 host ports plus 8 SAN Volume Controller ports. When it is possible, place each HBA port in a host that connects to a node into a separate zone. Include exactly one port from each node in the I/O groups that are associated with this host. This type of host zoning is not mandatory, but is preferred for smaller configurations.

Note: If the switch vendor recommends fewer ports per zone for a particular SAN, the rules that are imposed by the vendor takes precedence over the SAN Volume Controller rules.

To obtain the best performance from a host with multiple fibre-channel ports, the zoning must ensure that each fibre-channel port of a host is zoned with a different group of SAN Volume Controller ports.

Clusters with more than 64 hosts

Each HBA port must be in a separate zone and each zone must contain exactly one port from each SAN Volume Controller node in each I/O group that the host accesses.

Note: A host can be associated with more than one I/O group and therefore access VDisks from different I/O groups in a SAN. However, this reduces the maximum number of hosts that can be used in the SAN. For example, if the same host uses VDisks in two different I/O groups, this consumes one of the 256 hosts in each I/O group. If each host accesses VDisks in every I/O group, there can be only 256 hosts in the configuration.