Shadow copies may be lost when you defragment a volume

Symptoms

When you run Disk Defragmenter on a volume with shadow copies activated, all or some of your shadow copies may be lost, starting with the oldest shadow copies.

After the shadow copies are lost, events that are similar to the following may be logged in the System log:

Cause

The System Shadow Copy provider uses a copy-on-write mechanism that operates at a 16-KB block level. This is independent of the file system's cluster allocation unit size. If the file system's cluster size is smaller than 16 KB, the System Shadow Copy provider cannot easily determine that disk defragmentation I/O is different from typical write I/O, and performs a copy-on-write operation. This might cause the Shadow Copy storage area to grow very quickly. If the storage area reaches its user-defined limit, the oldest shadow copies are deleted first.

Resolution

If the file system's cluster size is 16 KB or larger, the provider can recognize disk defragmentation I/O and handle it correctly. Microsoft recommends that you use a 16-KB or larger cluster allocation unit size when you format the volume if you plan to defragment volumes that are used for shadow copies of shared folders, .

More Information

For more information about cluster allocation unit sizes, click the following article number to view the article in the Microsoft Knowledge Base:

140365 Default cluster size for FAT and NTFS

For additional information about best practices for using shadow copies of shared folders, see the "Shadow Copies of Shared Folders: Best Practices" topic in the Windows Server 2003 Help and Support Center.
Propiedades

Id. de artículo: 312067 - Última revisión: 7 ene. 2008 - Revisión: 1

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