Altaro Blog Post – Hyper-V Guest Design: Fixed vs. Dynamic VHD

I still encounter people who are confused by the disk options in Hyper-V.  Altaro have updated their blog with a post, discussing the merits of passthrough (raw) disk, fixed VHD, and dynamic VHD and it’s worth a read.  Being a storage company, it’s worth paying attention to their observations.

Further to their notes I’d add:

  • Windows Server 2012 adds a new VHDX format that is 4K aligned and expands out to 64 TB (VHD max is 2040 GB and VMDK is 2 TB).
  • Storage level backup cannot be done using passthrough disks so you have to revert to traditional backup processes.
  • Passthrough disks lock your VM into a physical location and you lose flexibility.
  • Advanced features like snapshots and Hyper-V Replica cannot be implemented with passthrough disks.
  • In production I always favour Fixed VHD over Dynamic.  However, I can understand if you choose Dynamic VHD for your OS VHDs (with no data at all) and place these onto a dedicated CSV (with no data VHDs on it) – assuming that data VHDs are fixed and placed on different CSVs.

Have a read of the Altaro post and make up your own mind.

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