vSAN Datastore has enough free space but cannot expand VM disk. Error thrown "Insufficient disk space on datastore 'vsanDatastore' .... "

Products

• VMware vSAN
• VMware vSAN 7.x
• VMware vSAN 8.x

Issue/Introduction

Affected Cluster Model: 2-Node Stretch/ROBO (2 Hosts, 1 Witness).  
While vSAN Datastore has plenty of free space, the disk of a VM cannot be expanded. The task fails with:
"Insufficient disk space on datastore 'vsanDatastore'. The disk extend operation failed: There is not enough space on the file system for the selected operation."

 

Environment

vSAN 7.x

vSAN 8.x

 

Cause

As shown via the Screenshot below:

 

Via the Fault Domain Setup, we do not see a Stretched Cluster configuration (= since button "Configure Stretched Cluster" does exist)

This means that this Cluster is not configured as 2-Node Stretch/ROBO Cluster ( = a Stretched Cluster Model )

 

As a result, this Cluster only consists of two Hosts and has no Witness Host

This is not considered as a functional vSAN Cluster and therefore the Cluster is unable to provide enough free space to execute the VM disk expansion successfully,

 

Resolution

Deploy a Witness Appliance and add it to the Cluster by configuring it as Stretched Cluster: 

 

1.) Review the Witness Host Requirements on page 7 of the Stretched Cluster Guide

 

2.) Download the OVA Template for the Witness Appliance by following KB 370026

( The OVA Template Build should be as close as possible to the Build of the existing vSAN Hosts currently in the cluster)

 

3.) Review the information on page 19 "Install a vSAN Witness Host Appliance" of Stretched Cluster Guide

 

4.) Deploy Witness Appliance by following steps outlined on page 4 of 2-Node Stretch/ROBO - Two Node Information

 

5.) Follow the Steps to configure your 2-Node Stretch/ROBO Cluster by following the steps under "Stretched Cluster Setup" starting on Page 9 of 2-Node Stretch/ROBO - Two Node Information

 

6.) Upgrade the Witness Appliance Build to the Build of your vSAN Hosts 
(= the Upgrade of a Witness Host is done the same way as you upgrade your vSphere ESXi Hosts)

 

If assistance is required, please open a Ticket with VMware by Broadcom Support.