vSAN -- Skyline Health -- Resync Operations Throttling

Products

• VMware vSAN

Issue/Introduction

Symptoms 

• If the Health Check fails, it indicates that the Host(s) listed under "Hosts with resync operation throttled"
  have the resynchronization bandwidth limit set to a specified value
  and shows an error when the value is less than 20 Mbps.
  As a result, Resync operations might be slow. 
• If the proactive network health check fails with Low bandwidth, that might point to the on-going resync and high bandwidth utilization 

This KB also talks about 

• Under vCenter Versions 6.5 & 6.7, it was possible to configure a bandwidth limit for Resync operations in the Web Client.
  
  
• The manual throttle of Resync has outlined above, has been deprecated with Version 7.0, due to the introduction of Adaptive Resync.

"vSAN 6.7 and newer contains a sophisticated method to balance the use of resources during times of resynchronization activities. Adaptive Resynchronization, or Adaptive Resync, optimizes vSAN’s ability to dynamically,
and transparently adapt I/O to best accommodate the needs of the virtual machines (VMs) against the tasks of the underlying storage system. This feature requires no manual configuration or intervention."

(Reference: Adaptive Resync in vSAN)

 

Environment

VMware vSAN 8.x
VMware vSAN 7.x
VMware vSAN 6.x

Resolution

Due to the introduction of Adaptive Resync, it is recommended to disable any manual configured Bandwidth Limitations unless these limitations are needed for particular cases like significant Resync traffic causing high VM latencies. 

In order to resolve the Warning "Resync Operations Throttling", the Resync Throttling needs to be manually disabled on the Hosts which are showing under "Hosts with resync operation throttled", by logging into the Host via SSH/Putty and run the following command:

# esxcfg-advcfg -s 0 /VSAN/DomCompResyncThrottle

Verify your change by running the following command:

 

# esxcfg-advcfg -g /VSAN/DomCompResyncThrottle

The output should show:

 

Value of DomCompResyncThrottle is 0

Alternatives:

• Run command if you see the above value reset on the hosts:
  
  esxcli vsan resync throttle set --level=0
• Use PowerCLI to set the value: Configuring resync throttle on a vSAN cluster via PowerCLI