Windows Server Technical Preview – Binary VM Configuration Files

Microsoft is changing the format of virtual machine configuration files by going back to the drawing board. There are two files in question:

  • .VMCX which is the virtual machine configuration file.
  • .VMRS which is for runtime state data

Both files are binary files; yes Microsoft is moving away from XML. And editing these files directly is strictly not supported – it never has been! You should use the admin tools, PowerShell, and WMI to edit a VM configuration.

There are two benefits to switching to binary files:

  • Performance: Reading from and writing to the files will become more efficient
  • Stability: There is a lower risk of corruption due to storage failure

This resiliency is being enabled by resilient logging of changes _ a change is written to the log, the log is replayed to the configuration file, and they clear away the log. And believe it or not, Microsoft has seen some customers where the XML format has caused performance bottlenecks!

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