Change Default Parameters for Latency Round Robin

On the ESXi host, you can activate the latency mechanism for the Round Robin path selection policy. The mechanism considers I/O bandwidth and path latency to select an optimal path for I/O. When using the latency mechanism, the Round Robin policy can dynamically select the optimal path and achieve better load balancing results.

When latency is activated, usage of paths for the I/Os depends on the workload. When a large number of paths is available, but the workload is not high enough, the system might not use some paths for I/Os.

You use the esxcli command to change the default parameters of the latency mechanism or deactivate the mechanism.

Prerequisites

Set the path selection policy to Round Robin. See Change the Path Selection Policy.

Procedure

1. Configure the latency mechanism by using the following command.

    esxcli storage nmp psp roundrobin deviceconfig set --type=latency --device=device ID

   The command takes the following parameters:

   Parameter	Description
   -S|--num-sampling-cycles=sampling value	When --type is set to latency, this parameter controls how many I/Os to use to calculate the average latency of each path. The default value of this parameter is 16.
   -T|--latency-eval-time=time in ms	When --type is set to latency, this parameter controls the frequency at which the latency of paths is updated. Default is 3 minutes.

2. Verify whether the latency Round Robin and its parameters are configured correctly.

    esxcli storage nmp psp roundrobin deviceconfig get --device=device ID

   or

    esxcli storage nmp device list --device=device ID

   The following sample output shows the path's configuration:

    Path Selection Policy: VMW_PSP_RR
      Path Selection Policy Device Config: {policy=latency,latencyEvalTime=180000,samplingCycles=16,curSamplingCycle=16,useANO=0; CurrentPath=vmhba1:C0:T0:L0: NumIOsPending=0,latency=0}
   

What to do next

To deactivate the latency mechanism, in the Advanced System Settings for your host, change the Misc.EnablePSPLatencyPolicy parameter to 0.