Overview


Remote Shared Virtual Disk (RSVD) Protocol is a block-based protocol first introduced in Windows 8.1/Windows Server 2012R2 to allow a client to access a shared virtual disk on a remote Server Message Block(SMB3) share and perform file operations. One key scenario that leverages the recent improvements in the SMB3 protocol is to store a virtual disk on an SMB3 share and access it using a UNC path name. Under those conditions, you’d expect RSVD protocol traffic to flow over the wire. In reality, one additional step is needed for that to happen.

In Windows, Hyper-V acts as a client to trigger MS-RSVD traffic. The key to note here is ‘shared’ storage. If you don’t enable the virtual disk as shared storage then SMB3 protocol data units (PDUs) will flow over the wire instead of RSVD PDUs tunneled over SMB3.

Procedure


The steps below show you how to trigger RSVD traffic using Hyper-V.

1. Launch Hyper-V Manager and browse to the settings of any existing VM.

2. Click on SCSI Controller and select Hard Drive, then click Add. Note: Virtual hard disks connected to an IDE controller can’t be shared.

3. Use the UNC path to specify the location of the virtual disk pointing to the file server. Note: This virtual hard disk has to reside on a Scale-out File System (SOFS) or Cluster Shared Volumes (CSV) or else you will get an error.


4. By default this virtual disk is not shared, so enable sharing by selecting Advanced Features of the hard drive added and check the Enable virtual hard disk sharing option.

  

Result

This virtual disk is now shared. If you observe the network traffic using a network monitoring tool like Microsoft Message Analyzer (MMA), you will find RSVD PDUs going over wire to this remote file share (file://test/testfolder/). Below is a screenshot of RSVD PDUs, parsed by MMA.


 

Resources

[MS-SMB2]: Server Message Block (SMB) Protocol Versions 2 and 3 –  https://msdn.microsoft.com/en-us/library/cc246482.aspx

[MS-RSVD]: Remote Shared Virtual Disk Protocol – https://msdn.microsoft.com/en-us/library/dn393384.aspx

Hyper-V on TechNet - https://technet.microsoft.com/en-us/library/hh831531.aspx   

Microsoft Message Analyzer (download) - http://www.microsoft.com/en-us/download/details.aspx?id=44226