You have a Windows Server 2008 R2 Hyper-V server. One of the virtual machines (VMs)
that is hosted on the server has a directly attached physical disk. You need to back up the
VM. What should you do?

A.
Perform a full server backup on the VM.

B.
Perform a critical-volume backup on the VM.

C.
Perform a full server backup on the host server.

D.
Perform a critical-volume backup on the host server.

Explanation:
Physical disks that are directly attached to a virtual machine. These disks cannot be backed
up by the Hyper-V VSS writer. As a result, this type of disk will not be included in any backup
performed by a backup program that uses the Hyper-V VSS writer. In this situation, you
would need to use some other process to back up the physical disk, such as running a
backup application within the guest operating system.
http://technet.microsoft.com/en-us/library/dd252619(v=ws.10).aspx
Hyper-V backups of Virtual Machines with pass through disks will show the error message
“One or more virtual machines have been excluded from the backup as the the virtual
machine uses one or more physical disks.
Use the Backup Exec Remote Agent on the virtual machine for backup and restore
operations.” Error 0xa0009644 – One or more virtual machines have been excluded from the
backup as the the virtual machine uses one or more physical disks. Use the Backup Exec
Remote Agent on the virtual machine for backup and restore operations.
Cause Pass Through Disk in Hyper-V : Hyper-V allows virtual machines to access storage
mapped directly to the Hyper-V server without requiring the volume be configured. The
storage can either be a physical disk internal to the Hyper-V server or it can be a Storage
Area Network (SAN) Logical Unit (LUN) mapped to the Hyper-V server. To ensure the Guest
has exclusive access to the storage, it must be placed in an Offline state from the Hyper-V
server perspective. Additionally, this raw piece of storage is not limited in size so,
hypothetically, it can be a multi-terabyte LUN.
Solution
As per the SCL (Software Compatibility List) the Pass Through is not supported if:
Physical(Pass Through) DAS or SAN on the Host directly attached to the Guest
Physical (Pass Through) RDAS on the Host directly attached to Guest
Guest Disk attached via SAN(iSCSI initiator)