VSS for ContinuousDataReplicator


VSS is utilized on the source computer for creating snapshots and the VSS writers are used for performing quiesce/unquiesce of Exchange and SQL data. VSS is also used for creating Recovery Points. For Windows 2000 or Windows XP, snapshots on the source computer during the SmartSync Scan phase are created by QSnap, and the default quiesce method is used for quiescing the applications. Recovery Point snapshots on the destination computer can be created using VSS to create Shadow Copies for the snapshots.

If the source computer has Commvault VSS Provider installed, then the VSS quiesce method is used to perform quiescing the applications. For Exchange and SQL Server's, Commvault VSS Provider is utilized on the source computer to perform an online quiesce/unquiesce, instead of using CDR's default offline quiesce/unquiesce, while a marker is placed in the log file for a Consistent Recovery Point. Online quiesce allows the server to continue to function with no interruption for users. If CDR VSS Provider is not installed then the legacy quiesce method is used for creating a Consistent Recovery Point.


The following is necessary to implement this functionality:

  1. Verify that the source or destination computer meets the System Requirements, and is a supported operating system platform and application server software for using VSS with CDR. Refer to ContinuousDataReplicator - Application Support.

  2. Install CDR software with the VSS Provider for CDR on the source and/or destination computer(s). Also, install CDR software on the destination computer; the VSS Provider for CDR is not required on the destination. For instructions, see Deployment - ContinuousDataReplicator.

  3. For a destination computer, to use VSS to create Shadow Copies for Recovery Points, right-click the Replication Set on the source computer and select Properties. In the Replication Options tab, select one of the choices in the Select Snap Engine Type for Recovery Point Creation section.


    If you have the hardware VSS provider setup as the default snap engine and you want to use Microsoft VSS for creating snapshots on the destination computer, you can use the nUseVSSSoftwareProvider additional setting. Note that the CDR services will need to be recycled on the client computer for changes to take affect.

VSS Considerations

Before using VSS, review the following information:

  • VSS is the default snap engine used on a Windows 2003 or higher source computer.

  • VSS is not available with Windows 2000. Do not specify VSS as the Snap Engine for a computer running Windows 2000.

  • The CDR VSS Provider is supported on a cluster and only needs to be installed on the physical node of a cluster.

  • The VSS Provider for CDR does not support multi-instancing. It must be installed on Instance001.

  • A VSS online quiesce ensures that users will not lose their connection to the server, e.g., Outlook clients will not be disconnected.

  • Exchange can be quiesced at the Storage Group level.

  • When creating Recovery Points using VSS, a maximum of 256 snapshots are allowed.

  • Recovery Point snapshots created with VSS can be deleted in any order.

  • The VSS cache can be configured using the vssadmin add shadowstorage command from a command line prompt. Refer to Microsoft documentation for details.

  • When using VSS, it is recommended that you do not start a large number of pairs, using the same source volume, simultaneously. To avoid any issues, you should vary the starting time for pairs which use the same source volume.

License Requirement

To perform a data protection operation using this Agent a specific Product License must be available in the CommServe® Server.

For general information about licenses, see the Commvault Licensing Program Guide. Also, Applying a License in the CommCell Console provides step-by-step instructions on how to view and apply licenses.

The VSS Provider for CDR does not require a license.