COPY Command Causes File Cache to Grow

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This article was previously published under Q163880

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SYMPTOMS

When you use the COPY command of Cmd.exe to copy files that are significantly larger than the physical memory, Windows NT appears to slow down and user interface performance decreases.

When you look at this in performance monitor, the cache is very large (from 50 to 90 percent of physical memory) and the process working sets have shrunk.

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MORE INFORMATION

The CreateFile API has a flag (FILE_FLAG_SEQUENTIAL_SCAN) that is useful when copying files. It tells Cache Manager to not grow the file cache when requests for this handle arrive. Therefore, Memory Manager does not have to shrink the application's working set to accommodate the larger cache. The CopyFile and CopyFileEx APIs make use of this flag.

Although the COPY command uses the CopyFile API, it opens the file without the mentioned flag first to inspect the source and destination files.

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WORKAROUND

Use XCOPY, File Manager or Windows Explorer to copy large files.

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RESOLUTION

To resolve this problem, obtain the hotfix mentioned below.

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STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. This problem was corrected in the latest Microsoft Windows NT 4.0 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

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