Physical planning requirements

Multisystem clustered environment (for switchable independent disk pools)

High-speed link (HSL) cables must be used to attach the expansion units to the servers in the cluster.

The expansion unit must be physically adjacent in the HSL loop to the alternate system or expansion unit owned by the alternative system. You can include a maximum of two servers (cluster nodes) on each HSL loop, though each server can be connected to multiple HSL loops. You can include a maximum of four expansion units on each HSL loop, though a maximum of three expansion units can be included on each loop segment. On an HSL loop containing two servers, two segments exist, separated by the two servers. All expansion units on one loop segment must be contained in the same device cluster resource group (CRG).

In order for an expansion unit to become switchable it must physically be the farthest away from the owning server on the loop segment.

Note: An error will occur if you try to make an expansion unit switchable if there is another expansion unit farther away the owning server that has not become switchable.

Figure 1. These expansion units are all private and are not switchable.

Figure 2. The expansion unit farthest away from the owning server on the loop segment has been made switchable.

The switchable expansion unit must be SPCN-cabled to the system unit that will initially serve as the primary node for the switchable hardware group (device CRG). The primary node might be a primary or secondary logical partition within the system unit. If using logical partitions, the system buses in the intended expansion unit must be owned and dedicated by the partition involved in the cluster.