Shadow copies may be lost when you defragment a volume (312067)

The information in this article applies to:

Microsoft Windows Server 2003, Standard Edition
Microsoft Windows Server 2003, Enterprise Edition
Microsoft Windows Server 2003, Datacenter Edition
Microsoft Windows Small Business Server 2003, Standard Edition
Microsoft Windows Small Business Server 2003, Premium Edition

This article was previously published under Q312067

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.

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 additional 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.

Modification Type:	Major	Last Reviewed:	9/11/2006
Keywords:	kbprb KB312067