VM Encapsulation

Encapsulation is one of the four key benefits of VMware virtual machines.  On the surface it may seem like this is a common feature across all virtualization platforms — but it’s not.

If you are a VMware ESX administrator, you know that a VMware virtual machine consists of several files,  normally contained in a single directory.  There is a configuration file, virtual disk files, and a few other supporting files.  Having all necessary VM files in one directory is the essence of encapsulation.

Let’s say that you have a development environment — not protected by VMware HA — that experiences a host failure.  You repair the host, reinstall ESX, and reattach the disk that contains your virtual machines.  In order to have ESX recognize a VM, it must be registered.  This is easily done with the Datastore Browser, just right-click on the .vmx file and select “Add to Inventory.”

This task can also be performed on the ESX service console (i.e., not ESXi) by using the vmware-cmd utility.  Here is an easy technique, just cd into the VM directory first:

vmware-cmd -s register $PWD/whatever.vmx

After that you are ready to power on your VMs and get back to work — snapshots and all.

Recovering Hyper-V VMs

Unfortunately, with Hyper-V you need to be more proactive — unless a VM is explicitly “exported” it cannot be “imported.”  There is no supported method of importing a VM from a failed host, especially if it has snapshots.  Or is that checkpoints?

Don’t believe me?

For the curious, there evidently is an unsupported technique to put Humpty Dumpty a Hyper-V VM back together again — for data recovery purposes only.  If making symlinks to XML files is your thing, go check it out.

When choosing a virtualization platform, don’t forget about the little things that can make a big difference.