32-Bit File Access Can Cause ScanDisk to Report Harmless Error

• Microsoft Windows for Workgroups version 3.11
• Microsoft MS-DOS operating system versions 6.2, 6.22

SYMPTOMS

After you run Windows for Workgroups version 3.11 on an MS-DOS 6.2 DoubleSpace-compressed drive or an MS-DOS 6.22 DriveSpace-compressed drive with 32-bit file access enabled, the MS-DOS ScanDisk utility may report the following error when run at the MS-DOS command prompt

   ScanDisk found <nnnn> bytes of data on drive <x> that might be one or
   more lost files or directories, but which is probably just taking
   up space.

NOTE: ScanDisk should not be run from the MS-DOS command prompt within Microsoft Windows or Windows for Workgroups. It should be run directly from MS-DOS. If you must run ScanDisk from within Windows, use the /CHECKONLY switch. This switch prevents ScanDisk from attempting to repair any damage while Windows is running.

CAUSE

This error message is caused by a problem in Windows for Workgroups 3.11. 32-bit file access writes buffers in the order they are used, meaning the first information into the buffer is the first information out. 32-bit file access also tries to improve access speed by finding contiguous used buffers and writing them together. If these two optimization schemes both try to clean the buffer simultaneously, an erroneous extra entry in the DoubleSpace or DriveSpace file allocation table (MDFAT) can occur.

This problem can also occur when 32-bit file access flushes the entire volume. Buffers are written sequentially according to their physical location. This optimization has no effect on a compressed volume (since there is no physical-to-logical relationship) and can result in erroneous entries in the MDFAT.

RESOLUTION

No saved data is lost. However, data in memory only at the time of the error message may be lost. If you choose to correct the problem, ScanDisk repairs the volume and creates the standard CHKDSK files (FILEnnnn.CHK), which can be deleted. ScanDisk may also report that there are sections of the DoubleSpace or DriveSpace volume not being used by any files but marked as unusable; it can repair these as well.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Windows for Workgroups version 3.11. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.