NTFS Uses CPU 100% While Allocating File Space

• Microsoft Windows NT Workstation versions 3.5, 3.51, and 4.0
• Microsoft Windows NT Server versions 3.5, 3.51, and 4.0

SYMPTOMS

You are copying large files (of 50 MB or more) from a computer running Windows 95 to a computer running Windows NT installed. You are moving the files with a drag-and-drop operation, using the Network Neighborhood tool or the My Computer tool in Windows 95. Windows NT CPU use increases to 100 percent, resulting in performance degradation and client disconnections.

CAUSE

The Network Neighborhood and My Computer tools in Windows 95 issue an SMBwrite of zero bytes at a file's new end-of-file (EOF) offset before actually writing data to the file. On large file systems that are highly fragmented, copying a large file can cause the Windows NT file system (NTFS) to use 100 percent of the CPU for an extended period of time. This can result in other threads being starved of CPU time, causing performance degradation and client disconnections.

This problem exists whenever a write of zero bytes occurs at a large offset beyond EOF on a highly fragmented file system as NTFS tries to allocate space to satisfy the request.

Using COPY/XCOPY from the DOS-PROMPT or copying to a FAT partition does not result in this behavior.

STATUS

Microsoft has confirmed this to be a problem in Windows NT versions 3.5, 3.51 and 4.0. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.