Performance Issues Hyper-V

System Enviroment:

Server01 - Windows 2008 R2, 2 x Quad Core Processors, 144GB RAM HP ProLiant

Server02 - Windows 2008 R2, 2 x Quad Core Processors, 144GB RAM HP ProLiant 

SAN01 - 8TB HP StorageWorks

SAN02 - 8TB HP StorageWorks

I have Server01 & SAN01 connected via ISCSI and 10 Virtual Machines running via Hyper-V

I have Server02 & SAN02 connected via ISCSI and 8 Virtual Machines running via Hyper-V

If I do any type of exports or disc expansions related to a Hyper-V machine the system in question becomes so slow that it almost comes to a stand still.

What could be causing the issue ?