The problem with 2gbsparse disks and vSphere

In the last several days I got a lot of problems with one of our customers and his VMs. It’s an outsourcing customer which used Hyper-V before the transition to our datacenter. As I heard (I was not involved in the project) there were several problems with converting some VMs from Hyper-V to vSphere. None of the traditional Converters worked (VMware Converter, Double Take, etc.). Somehow the team managed to convert these VMs but ended up in a 2gbsparse disk format which is only supported on hosted desktop platforms (VMware Workstation, Player, Fusion) and not supported as VMFS disk format.
After an Update to vSphere 5.1 the power-on process of these VM’s results in the following error message:

The system cannot find the file specified.

After a lot of research I found this VMware KB Article, which was not exactlly the solution, but under the additional information section, we found a command which solved the problem:

esxcfg-module multiextent

This command loads the kernel module multiextent that can interpret 2gbsparse vmdk files.
But why do we have to load the module manually after an upgrade to vSphere 5.1 Update 1? In earlier versions we saw that the multiextent module was loaded at startup.
Now it was time to look at the Release Notes of 5.1 and there we found some answers:
But this was also a dissatisfying answer. Our last hint we found in this VMware Article. The multiextent vmkernel module is no longer loaded by default with the following versions and later:

  • ESX/ESXi 4.1 Patch 8 (Build 1050704)
  • ESXi 5.0 Patch 5 (Build 1024429)
  • ESXi 5.1

A 2gbsparse disk format vmdk is not supported with vSphere. There are 2 ways to solve this problem permanently:

From my point of view the easiest way is to use VMware Converter Standalone, because if something goes wrong the original VM is not touched.

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