vCenter is not accessible and VMs down in vSAN cluster.

Products

• VMware vSAN

Issue/Introduction

Symptoms:

• Multiple virtual machines in a vSAN cluster appear as Inaccessible or Invalid.

• The vCenter Server VM is offline, and the vSphere Client (UI) is inaccessible.

• ESXi hosts report a vSAN Network Partition, where esxcli vsan cluster get shows a "Local Node State" as Master but a "Sub-cluster Member Count" of 1.

[root@ESX01 :~ ] esxcli vsan cluster get
Cluster Information
Enabled: true
Current Local Time: 2025-11-13T02:09:44Z
Local Node UUID: #######-####-####-####-###########
Local Node Type: NORMAL
Local Node State: MASTER
Local Node Health State: HEALTHY
Sub-Cluster Master UUID: #######-####-####-####-###########
Sub-Cluster Backup UUID:
Sub-Cluster UUID: #######-####-####-####-###########
Sub-Cluster Membership Entry Revision: 3
Sub-Cluster Member Count: 1
Sub-Cluster Member UUIDs: #######-####-####-####-###########
Sub-Cluster Member HostNames: ESX01
Sub-Cluster Membership UUID: #######-####-####-####-###########
Unicast Mode Enabled: true
Maintenance Mode State: OFF
Config Generation: #######-####-####-####-########### 8 2025-11-12T22:29:47.46
Mode: REGULAR
vSAN ESA Enabled: false

Environment

VMware vSAN 7.x
VMware vSAN 8.x

Cause

The issue is caused by the failure of communication between vSAN hosts, and assigned vSAN vmnic reporting as 'void' in esxtop.
In esxtop, an interface appearing as "void" indicates that the physical NIC has experienced a "Link Down"or a driver/firmware crash, causing the VMkernel to lose its uplink to the physical switch.
Where vmk4 used for vSAN traffic communication.

Reference:
[root@ESX01 :~  ] vmkping -I vmkl 192.##. ##.110
PING 192.##.##.110 (192.##.##.110): 56 data bytes
sendto () failed (Host is down)

Resolution

Engage networking team to check the physical status of the NIC card for any hardware failures, faulty SFP modules, or damaged cables.

Alternatively,

• If the secondary NIC is functional, set it as active until the issue with the primary NIC is resolved.
• Enable the vSAN traffic on a functional VMkernel adapter (vmk) until the underlying networking issue is resolved.