vSAN 7.0 Resync Throttling

How to throttle vSAN resync traffic in vSphere 7.0.

Resync throttling has been a feature of vSAN since version 6.6 (April 2017) and the functionality to set it existed in the vSphere Client GUI through to 6.7 before it was removed. However, you still have the ability to perform this throttling using PowerCLI. There is one warning: Don’t do it, unless you really have to - misconfiguration using this setting was causing more harm than good, hence the removal of the option in the vSphere Client. In the vast majority of situations vSAN’s quality of service systems should automatically throttle to ensure VMs are not impacted.

  1. Download the attachment configure-resync-throttle.zip from the VMware KB article Configuring resync throttle on a vSAN cluster via PowerCLI (83742), and whilst there note the instructions in that article for turning off resync throttling (that’s how you’ll revert this change). Unzip the PowerShell script in the download into the current directory.
  2. Open a PowerShell session and connect to vCenter
1Connect-VIServer MyvCenter.example.com
  1. Run the script, providing values for the vSAN Cluster name and the throttling level to set (1-512 Mbps)
1.\configure-resync-throttle.ps1 -Cluster "MyCluster" -Value 50

Note that the KB article says you must be running at least PowerCLI 12.2 for this to run, but I’d recommend at least 12.6 as that version resolves a bug in certain versions of PowerShell where Get-VsanView throws an error message of Object reference not set to an instance of an object which stops this code from executing.

Rather than cluster-wide this setting can also be applied to an individual host, either by connecting to a host rather than a vCenter with the PowerCLI above, or by opening a session on the host via SSH and using esxcli as follows:

1> esxcli vsan resync throttle get
2   Level: 50 Mbps
3> esxcli vsan resync throttle set 35

Skyline health checks will show a warning when resync throttling is configured and an error when the value is set to less than 20 Mbps.

Again- please be very careful using these tools (and read my disclaimer), and if in any doubt at all then don’t touch it and just contact VMware support.