The fast recovery components
Creation of Shadow Copies
As I stated earlier, the process of creation initiates by the requestor (a backup program) contacting the Volume Shadow Copy Service (VSC service) to request a copy of the System State. The VSC service will act as a coordinator and notifies the System State writers to prepare for writing data for creation of a shadow copy.
Once the data is ready for the actual backup process each writer notifies the VSC service which then relays information to the backup requestor. Next step is that the requestor halts Active Directory I/O writes as long as it takes the provider to create single point-in-time copies of the three volumes. Usually this takes just a few seconds and should have no to little impact on Active Directory operations.
After the copy is made the VSC service will be instructed to break the connection with the original and the copy. At this point the shadow copy becomes read-only and the original will continue as usual (read/write). Now we are at the point where the shadow copy is no longer associated with a particular server and resides on the SAN until we need it.