Taking snapshots of VMware ESX 4 running in a VM

Clearly, the capability introduced with VMware vSphere 4 that allows VMware ESX 4 to virtualize itself is a real crowd-pleaser.

However, one limitation that some have discovered while using this lab-testing technique is the lack of ability to use snapshots with virtual ESX systems.  In fact, after taking a snapshot of a virtual ESX VM, you will see the system boot into the recovery shell like so:

Ouch.

Can we fix it?

I asked some super-smart engineers inside VMware about the issue, and of course they know all about it and how to make it work.

The solution is to enable an undocumented advanced configuration option on the physical ESX host like so:

In other words:

• Log into the console of the physical VMware ESX 4 host
• Run the following command: esxcfg-advcfg -s 1  /COW/PermitVmfsOnRedoHierarchy
• Verify the setting with the “get” flag: esxcfg-advcfg -g /COW/PermitVmfsOnRedoHierarchy

Do I even need to say that this stuff is not supported by VMware Global Support Services (GSS)?  Well, I just did.

Yes we can!

After executing that one command on your physical machine, take a snapshot and boot up your virtual ESX:

Everything works just like you need it to now — you can even create a snapshot hierarchy:

Now what?

Were you constrained by the lack of virtual ESX snapshots?  What interesting things will you use this for?

Related posts:

1. Half the VM reboots on Patch Tuesday
2. Hyper-V snapshots: not for production
3. VMware vSphere 4 has a Snapshot Alarm
4. IGT Part 5: Hyper-V snapshots are not gone until the VM is powered off