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10 Deploying Symantec Backup Exec 2014 with Dell PS Series Arrays | TR1057
2.1 VSS snapshots and backup
Snapshots (also called shadow copies) are point-in-time copies of data. A snapshot enables you to quickly
copy data at the disk volume level. This volume copy can then be used as the source for backup
operations. Snapshot creation does not disrupt access to the volume. The copy is created, typically in a
few seconds, and maintained in disk storage (for example, in a PS Series group), providing high
performance and low space utilization.
When using snapshots to backup data, the snapshot capability must be integrated with the backup
application, the applications and file systems to be backed up, and the storage devices. Historically, this
integration has required using custom scripts, which are difficult to create and maintain for proper
operation over time. These requirements have severely restricted the adoption of snapshot-based
backups.
Microsoft has a technology in Windows Server called Volume Shadow Copy Service (VSS). VSS provides a
framework for creating snapshots that integrates VSS-aware disk storage (for example, PS Series arrays),
applications (for example, Exchange or SharePoint), and operating system drivers, delivering a turn-key
backup solution to IT departments without the need for scripting.
There are three required components in the VSS framework as illustrated in Figure 2.
VSS writer (1): A business application (such as a database application, e-mail, or file system) that prepares
the application for snapshot creation or data restoration (for example, by flushing buffers, switching logs,
etc.). Hyper-V, NTFS, Exchange, SharePoint, and SQL are examples of VSS writers.
VSS requestor (2): Requests the creation of snapshots, typically for backup operations. Symantec Backup
Exec 2014 supports VSS and can be used as a VSS requestor.
VSS provider (3): The mechanism that actually creates and maintains the snapshot in the storage
hardware. For example, the HIT kit installs a VSS provider that can create snapshots in a PS Series group.