Volume Shadow Copy Services (VSS) is a service in Microsoft Windows server that allows an application to take a consistent point-in-time copy (snapshot, etc.) of the whole application (e.g., multiple volumes). VSS freezes updates, and pushes all buffered data out to disk. This take a few seconds to a few minutes to evoke.
Several years ago, Microsoft indicated that VSS was to be the future of its data protection methodology and the Microsoft ecosystem has hopped on board. For example, many organizations use VSS to make point-in-time backups of an Exchange database (EDB) using third-party backup software. The VSS framework has evolved but it took some time as, early on, many said VSS was not robust enough for many demanding enterprises.
The VSS framework has three main parts:
- A Requestor, which initiates and controls the creation of a copy of the EDB (typically a backup software application);
- A Writer, which does all the database housekeeping to prepare the EDB for a copy (typically the Exchange database or SQL); and,
- A Provider, which handles the actual copy function itself (typically an external storage array).
The backup ecosystem comprises Microsoft, third party backup providers, and array vendors and has evolved over time. Early on, many users were uncomfortable betting the farm on VSS, and this slowed the adoption of next generation data protection approaches (e.g. in Exchange 2007 environments). The industry pushed Microsoft (and itself) to increase the sophistication of VSS in general and storage providers specifically worked hard to understand Exchange use cases and customer requirements.
NetApp for example, has a set of Snapshot managers that interface with VSS and help create consistent snapshots for Oracle, Exchange, etc.
Users can also take non-VSS crash consistent snapshots - a point in time, but the data on the disk is not guaranteed to be consistent with (say) the log file. It takes longer to reprocess the log file to bring the application up. However, it is quicker to take the snapshot.
Action Item: Microsoft's VSS framework represents an opportunity for backup vendors and array companies to partner with Microsoft to advance copy services and near continuous data protection. However the industry in general and Microsoft in particular must continue to aggressively push the sophistication of VSS and integrate within Microsoft environments. Only when users have good visibility that this framework will meet future business requirements should they standardize on a VSS methodology within their organizations.