2 Node vSAN cluster shows VMs with reduced availability

Products

• VMware vSAN

Issue/Introduction

The purpose of this KB article is to advise the best course of action when the objects have reduced availability due to discrepancies in the disk format version.

Symptoms:

• All of the vms on the host have the warning "reduced availability with no rebuild"
• "Repair objects immediately" option on the vsan health does not rectify this issue
• Clomd.log logs the following message upon trying to repair:

"The version mismatch is from the witness which is on version v3 the data nodes are on version v5
YYYY-MM-DDT06:01:02.595Z 327036 (1072927856928)(opID:1804363429)CLOM_LogOpReport: OpReport: type:10 status:Not found reason:13
YYYY-MM-DDT06:01:02.595Z 327036 Total nodes:3 Total disks:17 disksUsed:0 phyDisksUsed:0 disksNeeded:1 disks decommisionning:0 disks with Node decommisionning:0 unhealthy disks:0 disks with unhealthy ssds or nodes:0 disks with insufficient space:0 disks with max components:0 disks with storage type mismatch:0 disks with version mismatch:1 disks in witness nodes:0 disk failed affinity/anti-affinity rule:0"

Environment

VMware vSAN 8.0.x
VMware vSAN 7.0.x
VMware vSAN 6.x

Cause

The cause of this issue is due to the fact that the witness appliance is not on the same disk format version as the two data nodes. In this instance/example in the symptoms, the data nodes are on disk format version 5 while the witness is on disk format version 3. This leads to a situation where the version 5 objects can not rebuild with a version 3 object.

Resolution

In order to resolve this issue please upgrade the witness appliance to a version where it can have a consistent/same disk format version with the data nodes.

More information about on-disk format versions can be found in the following KB.
Understanding vSAN on-disk format versions and compatibility

Additional Information

Impact/Risks:
In the case of a failure the version 3 objects could not be used to rebuild the objects. This can also cause the witness node to be isolated from the cluster.