Recently with a Hyper-V 2012 implementation I came across an issues where Live Storage Migrations would stop at 99% and would inevitably fail.
The customer was using Dell Compellent Shared Storage with iSCSI connectivity.
The Dell Compellent Storage supported ODX functionality and thus ODX functionality in Windows Server 2012 was enabled.
This issue was resolved with the following Microsoft Hotfix:
Offloaded Data Transfers fail on a computer that is running Windows 8 or Windows Server 2012