Cluster partition issue observed after adding a host to the existing vSAN cluster
Article ID: 413293
Updated On:
Products
Issue/Introduction
Symptoms:
- Newly added host shows partitioned in the vSAN cluster.
[root@esxi :~ ] esxcli vsan cluster get
Cluster Information
Enabled: true
Current Local Time: 2025-10-06T01:44:05Z
Local Node UUID: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx
Local Node Type: NORMAL
Local Node State: MASTER
Local Node Health State: HEALTHY
Sub-Cluster Master UUID: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx
Sub-Cluster Backup UUID:
Sub-Cluster UUID: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx
Sub-Cluster Membership Entry Revision: 0
Sub-Cluster Member Count: 1
Sub-Cluster Member UUIDs: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx
Sub-Cluster Member HostNames: esxi
Sub-Cluster Membership UUID: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx
Unicast Mode Enabled: true
Maintenance Mode State: OFF
Config Generation: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx 8 2025-10-06T00:44:32.487
Mode: REGULAR
vSAN ESA Enabled: false
- The vSAN network configuration is in place:
[root@esxi :~ ] esxcli vsan network list
Interface
VmkNic Name: vmk1
IP Protocol: IP
Interface UUID: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx
Agent Group Multicast Address: x.x.x.x
Agent Group IPv6 Multicast Address: ff19: :x:x:x
Agent Group Multicast Port: 23451
Master Group Multicast Address: 224.x.x.x
Master Group IPv6 Multicast Address: ff19 :: x:x:x
Master Group Multicast Port: 12345
Host Unicast Channel Bound Port: 12321
Data-in-Transit Encryption Key Exchange Port: 0
Multicast TTL: 5
Traffic Type: vsan
[root@esxi :~ ]
- Ping test is also working without issues:
[root@esxi :~ ] vmkping -I vmkl x.x.x.x
PING x.x.x.x (x.x.x.x): 56 data bytes
64 bytes from x.x.x.x: icmp seq=0 ttl=64 time=0.388 ms
64 bytes from x.x.x.x: icmp seq=1 ttl=64 time=0.421 ms
64 bytes from x.x.x.x: icmp seq=2 ttl=64 time=0.486 ms
x.x.x.x ping statistics -
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.388/0.432/0.486 ms
Environment
VMware vSAN 7.x
VMware vSAN 8.x
Cause
The unicast table on the existing hosts not updated properly could lead to this issue. The unicast table should always show the details of all the other hosts except itself.
If there is a 4-node cluster, each host should have 3 entries in the unicast table. Having any less (like shown below) could cause cluster partition issues.
[root@esxi01:/vmfs/volumes/6672dfa0-b56539b3-a412-xxxxxxxxxxxx/log/log_dump/esxi] localcli vsan cluster unicastagent listNodeUuid IsWitness Supports Unicast IP Address Port Iface Name Cert Thumbprint SubClusterUuid------------------------------------ --------- ---------------- ------------- ----- ---------- ----------------------------------------------------------------------------------------------- --------------6688178a-xxxx-xxxx-xxxx-0050xxxxxxxx 0 true 192.xxx.x.xxx 12321 60:29 5203f040-xxxx-xxxx-xxxx-4bxxxxxxxx6688178b-xxxx-xxxx-xxxx-0050xxxxxxxx 0 true 192.xxx.x.xxx 12321 C3:28 5203f040-xxxx-xxxx-xxxx-4bxxxxxxxx
The reason why the unicast table does not automatically update after adding a host to the vSAN cluster could be if the IgnoreClusterMemberListUpdates parameter is set to 1.
[root@localhost :~ ] esxcfg-advcfg -g /VSAN/IgnoreClusterMemberListupdatesValue of IgnoreClusterMemberListUpdates is 1
With the parameter set to 1, the hosts will not update the cluster information is any new hosts are added to the cluster.
Resolution
Reset the IgnoreClusterMemberListUpdates parameter to the default value of 0 by using the below command:
esxcfg-advcfg -s 0 /VSAN/IgnoreClusterMemberListUpdates
Verify if the value is successfully changed by using the below command:
esxcfg-advcfg -g /VSAN/IgnoreClusterMemberListUpdates
The partition issue should be resolved after this.
Additional Information
If in case, the unicast table does not populate on its own, kindly use the below KB article to manually update it:
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