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Full Title: When you remove a virtual hard disk from a virtual machine in System Center Virtual Machine Manager 2008 R2, the .vhd file on the Hyper-V server is deleted without warning
In Microsoft System Center Virtual Machine Manager 2008 R2, you remove a virtual hard disk (VHD) from a virtual machine. You expect that the .vhd file is detached from the virtual machine. However, the .vhd file is actually deleted on the Hyper-V server.
http://support.microsoft.com/?kbid=976246
Read the complete post at http://wmug.co.uk/blogs/cliffs_blog/archive/2009/11/16/ms-kbs-when-you-remove-a-virtual-hard-disk-from-a-virtual-machine-in-system-center-virtual-machine-manager-2008-r2-the-vhd-file-on.aspx