Using Differencing Disks with Hyper-V VDI

When using virtual desktop pools with Microsoft VDI, a single desktop image is shared among many users. Pooled desktop images are used for a predetermined time, which is usually the life of their session. After their predetermined time, usage of the image is over, and the disk image is restored back to its original state and any changes during the session are erased. That is, unless you use differencing disks. However, there are pros and cons to using differencing disks:

Storage Container

Pros

Cons

Differencing VHD

*note: dynamic disks face many of the same performance issues that differencing disks face

  • Good performance
  • Quicker to create than fixed sized VHD
  • Grow dynamically to save disk space and provide efficient storage usage
  • Smaller VHD file size makes it more nimble in terms of transporting across the network
  • Blocks of full zeros will not get allocated and thus save the space under certain circumstances
  • Compact operation is available to reduce the actual physical file size
  • Interweaving of metadata and data blocks may cause I/O alignment issues
  • Write performance may suffer during VHD expansion
  • Dynamically expanding and differencing VHDs cannot exceed 2040 GB
  • May get VM paused or VHD yanked out if disk space is running out due to the dynamic growth
  • Shrinking the virtual capacity is not supported
  • Expanding is not available for differencing VHDs due to the inherent size limitation of parent disk
  • Defrag is not recommended due to inherent re-directional layer

For more information about using differencing disks with Microsoft VDI, continue at source…

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