Which Windows Server Virtualization 08 (code named Viridian) storage is best for you?

If you have had a chance to play around with our prerelease bits you might be wondering what all the types of storage are. You might also be wondering how to decide which storage is right for your virtual machine (VM). One question I'll address in a future blog posting is storage performance. Its a little early to talk performance with prerelease bits but rest assured we are working hard to drive much better performance.

  So what type of storage is there?

  • (dynamic / Fixed) Virtual Hard Drive (VHD) - This is a file stored in NTFS that looks like hard drive to the VM
  • Delta VHD - This stores all changes relative to a base VHD.
  • Pass-through drives - Pass-through drive are physical disks are exclusively assigned to the VM.

There is also another dimension to consider

  • Synthetic Devices - These are new with Viridian. These devices communicate over VMBUS (future post) with the root (sometimes called the host) partition. These devices have an advantage over emulated devices because they better leverage the existing Windows driver architecture.
  • Emulated Devices - These devices try to emulate well know devices like disk, video, etc. These are less performant than Synthetic Devices because of their emulation.

 An overview of pros and cons…

Storage Type



Dynamic VHD

Don’t have to decide the size of the disk upfront

Not as performant as Fixed VHD

Fixed VHD

Best performance for file based hard drives

Fills up

Delta VHD

Great for deployment of base golden image

Read might have to access delta and fixed drive + more file overhead.


Attach a physical drive / LUN to a VM


Does not support Virtual Machine Snapshots + no easy as easy to move as a VHD. This is great for direct attached storage however.


Tricky configuration. You have to take the drive offline in the root partition before it can be configured to a VM. Use Disk Manager (diskmgmt.msc), diskpart.exe, …


So which storage is best for you? You’ll like this answer – It depends J

We expect Fixed VHD and Pass-through to be the most common in deployment because of their predictable nature.

[[Since this is a CTP all these behaviors might change and there are no promises or warrantees it will continue to work this way]]