Planning for a direct-attached configuration

A direct-attached configuration dedicates entire port bandwidth to be used for a specific connection. Planning must account for the volume of expected traffic before you decide how many ports are used in a direct-attached configuration. Direct attached connections are supported on the same speed at both ends.

The system offers multiple options in deciding how to create a direct-attached configuration. Bandwidth requirements for a direct-attached configuration make it important to determine the volume of expected traffic in deciding the number of ports. Ensure you have accounted for sufficient bandwidth, in particular node to node as the bandwidth between nodes determines write speed for replicated workloads.

For example, if a system to system direct-attached link is configured between nodes in an I/O group, then the link carries cache replication traffic and it might carry inter-node traffic such as FlashCopy data. Hence, enough system to system bandwidth needs to be available so that:
  • Cache replication for host writes can occur without any bandwidth bottleneck
  • All possible intra-node traffic can be carried without any bandwidth bottleneck.
The following guidelines are provided for direct-attached configurations.
  1. Fibre Channel direct attachment to host systems.

    The system allows direct attachment connectivity between its Fibre Channel ports and host ports. Host systems can be connected to 16 Gbps to 64 Gbps Fibre Channel ports on the system. No special configuration is needed for host systems that are using this configuration.

    For more information about host compatibility, see IBM System Storage Interoperation Center (SSIC).

  2. Fibre Channel direct attachment between nodes in a system.

    Direct connection of the system Fibre Channel ports without using a Fibre Channel switch is supported. Such direct connections between the system nodes might be useful in small configurations where no Fibre Channel switch exists. It can also be used to connect nodes in the same I/O group to provide a dedicated connection for mirroring the fast write cache data. Ensure that sufficient bandwidth is provisioned between nodes to accommodate all the intra-node traffic.

Note: Direct attached connections are supported on the same speed at both ends.