Considerations When Using Pass-Through Physical Disks Or Vhds - Dell PowerVault MD3200 Series White Paper

Planning for Hyper-V: PowerVault™ MD3200 and MD3200i Series of Arrays
VHDs have several different options:
•
Dynamic expansion – The VHD file grows as data is stored to the physical disk, with a
maximum size not exceeding the size specified during creation. When using the New
Virtual Machine Wizard in the Hyper-V Manager, select Dynamically Expanding when
you create a new VM.
•
Fixed size – The VHD file uses the full amount of space specified during creation.
•
Differencing – The VHD file exists as a child disk in a parent/child relationship with an
existing VHD. The parent VHD is left intact, and changes that occur are stored on the
child (differencing) VHD.
Note: For the best performance in production environments, use fixed-size VHDs because
they eliminate the overhead created by expanding the VHD in a normal production
environment.
Size each LUN to support the target VHD. To avoid warning messages generated by the parent partition
about the physical disk running out of capacity, allocate an additional 200 MB to the LUN, and leave
this additional 200 MB as empty space on the virtual disk.

Considerations When Using Pass-Through Physical Disks or VHDs

Keep the following considerations in mind when you use pass-through physical disks or VHDs:
•
VHDs support the ability to export the drive to another parent server.
•
VHDs support VM checkpoints.
•
Pass-through physical disks offer slightly higher performance than VHDs and support
virtual disk sizes larger than 2 TB. However, pass-through physical disks do not support
VSS-based backup or checkpoints. VSS-based backups with hardware providers work as
long as the backups are initiated from the parent. Inside the VM, only software-based
VSS backup is supported.
•
You can use both VHDs and pass-through physical disks in clustered environments.
LUN1 – VHD Method
LUN2 – Pass-Through Method
LUN3 – Storage Direct Method
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