Identify Enhanced Round Robin Load Balancing (Latency Based PSP)

Products

• VMware vSphere ESXi

Issue/Introduction

Check if devices are set with Enhanced Round Robin Load Balancing (Latency Based PSP).

Environment

ESXi 6.7

ESXi 7.0

ESXi 8.0

Cause

In vSphere 6.7 U1, we introduced a new sub-policy for the Round Robin (RR) Path Selection Policy (PSP) VMW_PSP_RR which actively monitors paths for latency and Outstanding IO, which is called Enhanced Round Robin Load Balancing (Latency Based PSP).  

When using the latency mechanism, the Round Robin policy will dynamically select the optimal path(s), in other words, it will monitor the paths to avoid a path that has higher latency or possibly HW issues, subsequently achieving better load-balancing as well as better performance.

 

For more details please visit Latency Round Robin Path Selection Policy.

 

 

Resolution

On vCenter UI, there is no differentiation in the name of the policy. You will always see "Round Robin (VMware)".

So to check if you are using the Enhanced Round Robin Load Balancing (Latency Based PSP), you have to run the command below in the host command line:

esxcli storage nmp device list

 

or per device:

 

esxcli storage nmp device list -d naa.xxxxxxxxxxxxxxx

 

 

You will see output similar to:

 

 

If you see "{policy=latency}", it means you are using the Enhanced Round Robin policy.

 

 

Furthermore, please note that this setting is per host and per device basis.