vSAN Datastore capacity incorrect due to cluster partition

Products

• VMware vSAN

Issue/Introduction

This article addresses a scenario where the vSAN datastore reports a significantly lower total capacity than the combined physical disks across all ESXi hosts. This usually occurs when a network partition prevents hosts from contributing their storage to the global datastore.

Symptoms

• The vSAN datastore reports a total capacity equal to the disks on a single host (e.g., 31 TB) instead of the combined total of all hosts (e.g., 90 TB).
• vSAN Skyline Health indicates a cluster partition where each ESXi host is isolated in its own partition.
• The unicast agent list on the ESXi hosts is empty, showing no peer entries.
• Virtual machine objects may show as inaccessible or reduced-availability-with-no-rebuild.
• Attempts to ping peer vSAN VMkernel interfaces with large packets (vmkping) may fail.

Environment

ESXi version 8.0 u3

Cause

A cluster partition is occurring because the ESXi hosts cannot establish vSAN network communication, often due to an empty or incorrect unicast agent list.

When a partition exists, vCenter Server displays capacity statistics from only one partition at a time, resulting in a size mismatch.

Resolution

1. Verify Cluster State: Run the following command on each host to check the partition status:

   localcli vsan cluster get

   Review the Sub-Cluster Member Count. If the count is 1, the host is isolated.
   
   

   Example of localcli vsan cluster get output during a partition:

   Cluster Information:   
   Enabled: true   
   Local Node State: MASTER   
   Sub-Cluster Member Count: 1
   Sub-Cluster Member HostNames: [HOSTNAME]

   
   
   
2. Validate Network Connectivity: Test the vSAN VMkernel port connectivity using vmkping with the MTU size used for vSAN (e.g., 8972 for MTU 9000):
   

   vmkping -I vmkX [IP_ADDRESS] -d -s 8972

   
   
   
3. Rebuild Unicast Agent List: Restore the unicast agent list on all affected hosts to enable peer discovery. Refer to Configuring vSAN Unicast networking from the command line for detailed steps.
   
   
   
4. Confirm Resolution: Once the lists are rebuilt, verify the Sub-Cluster Member count has increased:

   esxcli vsan cluster get

    

The vSAN datastore capacity should now reflect the combined total of all contributing hosts.