Deployment Considerations - IBM BladeCenters

When deploying Coherence on IBM BladeCenters please be aware of the following:

MAC Address Uniformity and Load Balancing

A typical deployment on a BladeCenter may include blades with two NICs where one is used for administration purposes and the other for cluster traffic. By default the MAC addresses assigned to the blades of a BladeCenter are uniform enough that the first NIC will generally have an even MAC address and the second will have an odd MAC address. If the BladeCenter's uplink to a central switch also has an even number of channels then layer 2 (MAC based) load balancing may prevent one set of NICs from making full use of the available uplink bandwidth as they will all be bound to either even or odd channels. This issue arises due to the assumption in the switch that MAC addresses are essentially random, which in BladeCenter's is untrue. Remedies to this situation include:

• Use layer 3 (IP based) load balancing, assuming that the IP addresses do not follow the same even/odd pattern.
  • This setting would need to be applied across all switches carrying cluster traffic.
• Randomize the MAC address assignments by swapping them between the first and second NIC on alternating machines.
  • Linux allows you to change a NIC's MAC address using the ifconfig command.
  • For other OSs custom tools may be available to perform the same task.