KB2796995 – Offloaded Data (ODX) Transfers Fail On A Windows 8 or Windows Server 2012 Computer

This is another recent KB article relevant to Hyper-V (and other scenarios) that I missed.  This one is for when file transfers via ODX fail on Win8 or WS2012 computers/hosts.


Consider the following scenario:

  • You create two Logic Unit Numbers (LUNs) on a third-party storage device.
  • You connect a computer that is running Windows 8 or Windows Server 2012 to the third-party storage device.
  • You assign the LUNs to the computer.
  • You copy a large amount of data by using the third-party storage device.
  • Then you use the Offloaded Data Transfers (ODX) feature to copy files from one LUN to another LUN.

In this scenario, the copy operation freezes at 99 percent.


This issue occurs because the copy engine incorrectly initializes regular copy chunks. Therefore, the copy engine restarts the entire copy process for the file when nonzero bytes are copied through the ODX. When the copy engine restarts, the destination file size is incorrectly set if all the following conditions are true:

  • The copy type is non-cached.
  • Nonzero bytes are copied through the ODX.
  • The file size is not aligned to a sector boundary.

Note The expected behaviour is that when nonzero bytes are copied through an ODX copy, the copy engine restarts a regular copy from where the ODX copy failed.

A supported hotfix is available from Microsoft

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