The VSS (Volume Shadow Copy Service) is a technology in Windows that allows the creation of backup copies or snapshots of computer data while it is in use. One of the most crucial features it offers is the ability to generate consistent snapshots, ensuring data integrity during the backup process.
Consistent snapshots are essential for applications and databases that rely on data consistency, such as transactional systems. This feature ensures that all changes made to the data are captured in a consistent state, preventing partial or corrupted backups.
Important: A VSS consistent snapshot guarantees that the application data, system files, and other critical resources are backed up in a stable and reliable state.
To achieve a consistent snapshot, the VSS process involves the following stages:
- Preparation: The VSS service notifies all applications and services that a snapshot is being taken.
- Freeze: All applications are frozen to ensure data consistency.
- Snapshot Creation: The snapshot is created, capturing the current state of the volume.
- Thaw: Applications are resumed, and regular operations continue.
Below is a comparison table of different types of VSS snapshots:
| Type | Description | Use Case |
|---|---|---|
| Application-consistent | Involves coordination with running applications to ensure data consistency. | Critical for database backups (e.g., SQL, Exchange). |
| Crash-consistent | Captures the volume in a state similar to a system crash. | Suitable for less critical applications, but may require recovery steps. |
| VSS-consistent | Captures the data while maintaining consistency, even in the event of application freezes. | Common in enterprise backup systems for critical operations. |