Balancing loads among available paths improves performance. If your array supports the ALUA protocol, your host uses that protocol to perform load balancing. If your array does not support the ALUA protocol and you want your host to do automatic load balancing, configure your devices to use the Round Robin PSP. If you want to do the load balancing yourself, you can perform manual load balancing.

With both active-active and active-passive storage arrays, you can set up your host to use different paths to different LUNs so that your adapters are being used evenly. If a path fails, the surviving paths carry all the traffic. Path failover might take a minute or more, because the SAN might converge with a new topology to try to restore service. This delay is necessary to allow the SAN to stabilize its configuration after topology changes.

You can configure your ESX/ESXi host to load balance traffic across multiple adapters by assigning preferred paths to your LUNs. Path policy must be set to Fixed.

The following example demonstrates how manual load balancing is performed with an active-active array.

Assume the following setup, shown in Manual Load Balancing with Fibre Channel.

Active/Active SPs

An ESX/ESXi system

Four Fibre Channel HBAs in each server

Director class software

Manual Load Balancing with Fibre Channel
Manual load balancing with four FC HBAs.

For load balancing, set the preferred paths as follows. Load balancing can be performed with as few as two HBAs, although this example uses four.

For LUN 1: HBA1-SP1-LUN1

For LUN 2: HBA2-SP1-LUN2

For LUN 3: HBA3-SP2-LUN3

For LUN 4: HBA4-SP2-LUN4

With active-passive arrays, you can perform load balancing if the array supports two active paths and the HBA ports can access both SPs in an array.

You can use the VMW_PSP_FIXED_AP path selection policies to do static path load balancing on active-passive arrays.