How can I recover a zero byte avhd file that should be several hundred gigabytes?

I have a SAN in operation with two LUN(s) and one of those luns is 9 terabytes.  This LUN is mounted via two nodes within a Hyper-V Cluster using a cluster shared volume.  Recently I discovered that a virtual machine failed and looking at the cluster shared volume ("C:\ClusterStorage\vmroot") I saw that the AVHD file (most recent snapshot) that should be several hundred gigabytes is now a 0 byte file.  It has become corrupt or something else has happened to it.  

     I unmounted that volume and that particular LUN is no longer being written to and no data has been written to C:\ClusterStorage\vmroot.  After copying the initial 0 byte avhd file to a remote share I opened the file in WinHex which revealed not much info at all.  It appears that the header isn't correct, however windows (2008 R2) does correctly show the filename.  It seems to me that the actual data should still be there on that LUN which happens to be a 6 disk raid 5 LUN.  

Does anyone have an idea on how to properly retrieve this data or is it even possible?
linuxroxAsked:
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
I know you do not want to hear this, but snapshots (AVHD) should never be able to run for more than 48 hours.

Microsoft does not support a VM, which is running on a snapshot for more than 48 hours, performance will be poor, and there is the chance of corruption.

Back to your issue, 0 byte Snapshot (AVHD) file, the data has been lost. So all data since the snapshot has been created has been lost, which could be many days, if you believe the snapshot should have gigs.

I would be inclined now to congtact a Data Recovery Specalist, such as Kroll Ontrack for Recovery.

There are not the cheapest, but can recover from these situations, if the data is important and you do not have a backup to restore.

http://www.krollontrack.co.uk/

To understand Hyper-V Snapshots further consult this article

Hyper-V Snapshots FAQ
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