If you find the inner workings of Exchange data backups using Volume Shadown Copy (VSS) a bit mystifying take comfort in not being alone. Administrators may ask, “What’s all the “freezing” and “thawing” I’m seeing in my event logs? What is the Exchange VSS Writer really, and what is it doing to my databases? How does it create a snapshot of a 135GB database in less than 60 seconds?”
If you ever asked these questions but only felt more confused with the answers, here’s a guide to clear some of that up. To understand how a VSS backup of Exchange works it’s critical to understand the basics of VSS itself. There is some excellent documentation on TechNet and MSDN on this, as well as the Windows Server Core Team blog, “Ask the Core Team.” My esteemed colleague Randy Monteleone sums up the basics of VSS very nicely early in his post, while also providing links (repeated here) to some good TechNet primers on VSS:
How To: VSS Tracing – Randy Monteleone
How Volume Shadow Copy Service Works
Volume Shadow Copy Service
If you’re already familiar with at least the basics of VSS, then look forward to Part 2 in this series, where we will break down the events that occur in a VSS Exchange backup, and how Exchange logs them in the application event log.
Read more at source: http://blogs.technet.com/b/exchange/archive/2012/06/04/everything-you-need-to-know-about-exchange-backups-part-1.aspx