Microsoft's Volume Shadow Copy Service (VSS) is Windows' built-in infrastructure for application backups. As a native Windows service, VSS facilitates creating a consistent view of application data during the course of a backup. VSS relies on coordination between VSS requestors, writers and providers for quiescence, or “to make quiet,” a disk volume, so that a backup can be successfully obtained without data corruption.
At least, that's the technical explanation — the one with all the big words. In simpler language, VSS is a Windows service that interacts with installed applications to tell them when a backup is taking place. It also reports back to the server when the backup is complete, instructing the application and the server to perform important post-backup tasks such as truncating logs and other cleanup activities.
Why is VSS necessary? Specifically, it is for coordination between the applications, their data and the activities being completed by your backup solution.
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