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Volume Shadow Copy Service (VSS) is a tool in Windows Server 2003 that makes periodic copies of files from shared folders, then stores these "shadow" copies for later retrieval. Many third-party backup and recovery products now employ VSS as an integral part of their operation.
Essentially, VSS provides a method of taking and storing snapshots of volumes in Windows. In the event of a major loss of data, the snapshots can be used for point-in-time re-creations of the entire volume, or else individual files can be extracted and restored as needed. As an added recovery feature, VSS keeps multiple shadow copies, providing the ability to restore at different points in time.
But problems can arise if the server in question has many shadow copies stored on the system, especially if the shadow copies are of large volumes, each containing many files. Eventually the paged pool memory may become exhausted.
One problem manifests itself when you try to delete multiple hardware shadow copy sets at the same time. An error occurs in the DeleteSnapshotSet() API and the delete operation fails.
Another potential -- and less obvious -- problem is that VSS does not maintain the name of the shadow copy device across the BreakSnapshotSet() API. If this were to happen, some software would probably break.
To fix this problem, Microsoft now has an update available. The Microsoft Knowledgebase article describes the problem and directs you to the appropriate update package for your version of Windows Server 2003.
As a bonus, this fix also removes a block that prevents administrators from creating and importing transportable shadow copies on some versions of Windows Server 2003 Enterprise and Datacenter editions. Once you install the fix, you can create and import transportable shadow copies.
Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in issues related to storage and storage management.
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