With the release of vCenter Server 6.0 Update 2a and ESXi 6.0 Patch 4 I decided it was time the update the lab environment. Both releases contain a lot of fixes, some specifically for VSAN.
The update went perfect on the Platform Service Controllers but then disaster struck. During the update of the vCenter Server the VM got a reset and the VM would not boot anymore with the error message:
“Error 15: Could not find file”
When using the Embedded Host Client to check the status of the VM I found out that the VM has had a reset started by the vpxuser. At first I suspected somebody else had giving the VM a restart but this was not the case.
Because I did not make a VM snapshot before the update (it’s a lab environment so he..) I could not recover the VM to a point before the update.
Luckily we had vSphere Replication configured for the vCenter Server to a different lab environment with PIT’s so I could recover the VM to an earlier state. After recovering the vCenter Server and logging on to the Web Client the cause of the reset was made clear.
Virtual Machine Monitoring was enabled for this cluster. Apparently no VMware Tools heartbeats have been received for 120 seconds (low sensivity) and no storage or network traffic was happening for a period of 120 seconds (default). This triggered a reset of the VM and therefore breaking it.
This vCenter Server has been upgraded several times and I never had any issue with VM Monitoring . I have no idea why this happened this time but to be sure I recommend disabling VM Monitoring for the vCenter Server during an update. And of course always have a backup of the vCenter Server in case of a failure.