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Learning Windows Server 2003 by Jonathan Hassell

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Using Shadow Copies

Shadow copies are a new technology within Windows products that enables a server to take snapshots of documents on a disk to record their states at certain points in time. If a user accidentally deletes or otherwise overwrites a file, he can open a version the server saved earlier in time, thereby eliminating the need for him to either re-create his work or contact the help desk to get them to restore the file from the most recent backup. When shadow copies are enabled on a disk, clients connecting to a share on that disk will be able to view and access previous point-in-time copies of either individual files or entire directories.

Further benefits lurk beneath the surface of this feature, however. The service behind shadow copies, called the Volume Shadow Copy Service (VSS), actually is responsible for a newly developed application programming interface (API) that allows server-based applications such as Exchange, SQL, and backup programs to take advantage of the benefits of shadow copies. Perhaps the most famous example is a backup that skips open files, either because they are currently open by a user or because they are locked by another process. In the past, this resulted in incomplete backups, either because the backup process halted in midstream because of this unrecoverable error, or because the process skipped the open file. If the open file is, say, your Exchange email database, that’s not necessarily a good thing. But now, with volume shadow copies, ...

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