In ESX 3.5, when trying to create a new snapshot, the following error is reported in the VI Client:

An invalid snapshot configuration was detected


Also, when reading the Virtual Machine log file (vmware.log) located in the same location as the VM, you may find references to delta files such as "vm_name-000001.vmdk", but when browsing the datastore, the delta file does not exists. Also, when running vmware-cmd hassnapshot,  "hassnapshot ()= " is returned, which means that the VM has no snapshots in place.

If this is truly the case, why is "An invalid snapshot configuration was detected" returned when trying to create a new snapshot?

VMware records snapshot information about the current VM in a .vmsd file. This file is located with the rest of the virtual machine configuration and VMDK files on the datastore. The file is normally called .vmsd. This file will contain information, even if your VM has no snapshots in place.

It is possible that in some cases, ESX fails to properly clean up after previous snapshots were removed. The information for previous snapshots may still be recorded in the .vmsd file. The file may indicate that you still have snapshots in pace, although all previous snapshots were removed and the dalta files have been merged. When you then try to create a snapshot, the .vmsd file will inform the ESX host that there is a delta file in place and that it has to create a second or third delta file. When the ESX host interigates the VMFS file system, it's unable to find the snapshot delta files specified in the .vmsd file and therefore errors with "an invalid snapshot configuration was detected."

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This is by no means a new issue. However, I still get support calls regarding tasks that get stuck on VMs. What do I mean by "stuck tasks"? Well, I've seen cases where a snapshot task initiated by VCB got stuck in the state of "Creating Virtual Machine Snapshot". Then VM goes down and cannot be accessed via the console, does not respond to pings, and the status of VMtools turns to "Unknown". You also cannot do "Power On" on the VM either as the "Creating Virtual Machine Snapshot" task is still showing as an active task. You can wait, but after 30 minutes, chances are that it won't sort itself out, so user intervention is required!

This is normally the approuch I take to sort this out:

1. Make sure that the VM is inaccessible to everyone and that it really is down.

2. Browse the datastore where the VM is located (best to do this via the CLI on the service console with "ls -lh") and check the time stamps of the files to see how log the snapshots, if any,have been sitting there for.
3. in VirtualCenter, or "vCenter" the VM will probably still be showing as powered on. Check on which of your ESX hosts it is running.
4. Log onto the service console of the ESX host that is running the VM. Elevate your priviledges to root.
5. Now, as the VM has an active task, you won't be able to send any other commands to the VM. You won't be able to use vmware-cmd to change the state of the VM either. Until the task that's stuck in progress has completed, the ESX host will not be able to send any power commands to the VM. The only way to now release the VM from it's sorry state and get rid of the "Active task" is to kill the VM's running process from the service console. In order to do so, you need to find the PID for the "running" VM. To get the PID do:

The Syntax is:
ps -auxwww |grep <VM-NAME>

Example:
Suppose you have a VM called WKSTNL01 The command will be:
ps -auxwww |grep WKSTNL01


This should return something like this:

root     12322  0.0  0.4   3140  1320 ?        S<s  13:32   0:03 /usr/lib/vmware/bin/vmkload_app --sched.group=host/user/pool1 /usr/lib/vmware/bin/vmware-vmx -ssched.group=host/user/pool1 -# name=VMware ESX;version=4.0.0;buildnumber=164009;licensename=VMware ESX Server;licenseversion=4.0 build-164009; -@ pipe=/tmp/vmhsdaemon-0/vmx673aca8b7403868b; /vmfs/volumes/489a1228-2bfd25b5-6a2c-000e0cc41e52/WKSTNL01/WKSTNL01.vmx

The PID in this instance is 12322. This is what we need to kill.

6. Kill the process ID with kill -9:

kill -9 12322


7. Delete any snapshots created

8. Power On the VM.

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