We had an incident couple weeks ago. A faulty node in a Windows 2008 R2 Hyper-V cluster caused the partition table lost in one of the CSV. Consequently, all the data can not be accessed.
I mounted the broken CSV LUN to another host with TestDisk installed. Then I used TestDisk to search and fix the broken partition table. After that, I mounted it back to the cluster. All data is back!! whew~
Here is the TestDisk step by step instruction. Easy but very useful!
Jackie Chen's IT Workshop 
Jackie,
Thank you so much, you saved our butts! We had a CSV that was corrupted with many important vm’s on it. This fixed it !
Hi Doug, you are welcome. Make sure you have a daily backup job running for those critical virtual machines. That is the safest way!
Thank you so much for your post! Totally saved my butt too. I had a Clustered Shared Volume partition full of Hyper-V VMs disappear off my md3000i last night after installing Windows 2008 R2 SP1 and a bunch of windows updates on the hosts. TestDisk worked like a champ and recovered my deleted/corrupt partition!
Redundant everything, but a disappearing partition on the SAN was the one point of failure I never planned on.