Practical Implications

High-end storage, which can track metadata on a per-sector basis, allows backup/restore operations to be more efficient by allowing changes to be tracked very closely and having backup operations deal with just changed data.

To be certain that a snapshot is consistent from an application's point of view, it is essential to have the operating system (including file systems) and the application participate in the process of flushing the cache and temporarily suspending write operations while the snapshot is made. The volume shadow copy service shipping with Windows Server 2003 pro¬vides the needed operating system and file system support, as well as architecture for the needed application support. Microsoft Exchange and Microsoft SQL Server are two important applications that will take advantage of this architecture.

It remains to be seen how quickly other vendors adopt and support the volume shadow copy architecture.

Summary

Backup operations have evolved in terms of both user requirements and the technology used to accomplish backups. Usage requirements have dictated that backups be made more frequently, yet without disrupting application access to data. Backup operations evolved from stand-alone backups to backup operations happening across a LAN to backup opera¬tions happening in a SAN environment. One problem that backup appli¬cations need to solve is backing up open files being accessed by active programs while the backup is being done.

In addition, backup applications have had to deal with a multitude of APIs that are specific to an application version and specific to an op¬erating system version. Yet another trend has been to create the initial backup from disk to disk, via a snapshot operation. Backup to tape is increasingly becoming a secondary backup operation, from the snapshot volume to tape.

The Windows volume shadow copy service provides an efficient way to create snapshots. The architecture provides for all important compo¬nents, including major applications such as databases and messaging servers to participate in the snapshot creation. Microsoft provides only the infrastructure to create a snapshot. Software vendors may use this infrastructure to build an application that can create and manage mul¬tiple snapshots.

Once a snapshot has been created, a backup may be created from the snapshot. Standard protocols such as NDMP may be used to accomplish the backup operation.

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