With the introduction of VSS, the purpose of making a full copy of the production data is obsolete. Using the VSS as a starting point, DPM provides an extremely fast and reliable change identification process.

DPM 2012 R2 relies on the VSS architecture and provides advanced change tracking functionality based on the mini-filter driver stack along with a DPM file filter.

The change identification process relies on VSS as the core component. Within the VSS architecture, there are three different snapshot technologies that you can use:

The Copy-on-write technique is the one that provides the possibility of making online snapshots during production hours. This technique identifies the block-level changes and "freezes" the blocks making them ready to be copied. If there are other blocks that were changed during that process, the VSS identifies those. Once the initial identification has finished, the VSS starts managing the changed blocks.

Describing the whole picture, there is more to it than just using the standard VSS architecture. Not only is Microsoft DPM dependent on the VSS functionality but it also uses parts from the mini-filter driver stack and a dedicated file filter named DPM file filter to make the change tracking process of block-level changes fully supported, as well as optimal and fast for a DPM protection scenario.

For further and deeper information regarding how Volume Shadow Copy Service works, refer the MSDN website http://msdn.microsoft.com/en-us/library/windows/desktop/bb968832(v=vs.85).aspx.

When DPM creates a recovery point, there are a number of underlying technologies that make it possible. As mentioned earlier in this chapter, the DPM server can take advantage of a system that uses transactional logs and adapt to the change journal. Creating a recovery point in DPM is a part of what Microsoft calls Express-Full. The Express-Full operation is the function that is triggered when the backup job is initiated from the DPM sever.

The Express-Full consists of the following: