Working with backup sets : VSS-aware backup sets (Windows) : About VSS-aware backup sets
 
About VSS-aware backup sets
VSS-aware backup sets use the target backup computer’s Microsoft VSS (Volume Shadow Copy Service) components to perform online backup. This kind of backup set is available in Windows DS-Clients only.
VSS-aware backup sets can be created for the following server types:
Microsoft Exchange Server
Microsoft Hyper-V Server (standalone or cluster)
Microsoft SharePoint Server
Microsoft SQL Server