Details on the New VZ VSS Driver

To overcome the current deficiency in the VMware VSS implementation for Windows 2003 and 2008 guest operating systems, Vizioncore is releasing its own VSS driver with vRanger Pro 4.5.

This driver is implemented as an .exe file which can be added to Windows 2003 and 2008 guests. When present, the vRanger Pro backup job invokes the VSS driver as part of the standard process for performing backup. As shown in the picture, the vRanger backup process does not change but operates to:

  1. Query for the VZ lock and add a lock to ensure that management processes do not collide in managing the image
  2. Invoke VSS -- which will either be the VSS built into the VMware platform OR the VZ VSS if it is present
  3. Invoke the VMware snapshot -- which releases the VMDK for backup or other types of management

Vizioncore VSS supports any VSS-aware application with two capabilities. First, it causes a brief queisce of the application database to write all data held in memory to disk. Any transactions held in memory are written and available for backup in the VMDK file. This ensures that the consistency point in the written data is current to a point-in-time just before the backup. After the backup is complete, the Vizioncore VSS also notifies VSS-aware applications that they have been backed up so that they can truncate their log files appropriately.

The VZ VSS capabilities are critical for Microsoft Exchange, in particular. To obtain the Exchange OLR capabilities which are offered as part of vRanger Pro 4.5, the VZ VSS must be present on the Exchange guest before backup.

SQL Server is not perfectly VSS-aware. As it turns out, some SQL Server administrators do not want SQL Server to truncate its log files after backup. Backup consistency, however, is assured with the VZ VSS driver.

It's helpful to know that without the VZ VSS driver, the consistency point captured from the VMDK in the backup is not likely to be from the current point in time. However, the VM is still recoverable and the application is still recoverable and usable. As part of recovery, the application would roll back to the most current consistency point held in its data. This could be from a point in time several hours before the backup was taken, depending on the operation of the application and how frequently transactions are committed to disk. This risk is that several hours of data could be lost.

The Vizioncore VSS driver is packaged with vRanger Pro 4.5, and comes with the download. The VSS driver is supported with vRanger Pro 4.2.3 as well as 4.5 versions.