Microsoft KB Archive/247575

= Chkdsk Does Not Use Backup Boot Sector to Fix Corrupted FAT32 Boot Sector =

Article ID: 247575

Article Last Modified on 3/1/2007

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APPLIES TO


 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows 2000 Professional Edition
 * Microsoft Windows 2000 Datacenter Server

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This article was previously published under Q247575



SYMPTOMS
If a FAT32 volume becomes corrupted or inaccessible and you attempt to repair the volume using the Chkdsk tool (Chkdsk.exe), the file system may be reported correctly as FAT32 (or possibly as RAW, depending on the damage), but the Chkdsk tool immediately quits without making repairs. For example, if you use the chkdsk e: /f command, the following message may be displayed:

The type of the file system is FAT32.

Volume Serial Number is C408-2213

If you run Chkdsk again without any command-line switches, it still shows the volume is corrupted. If you use the chkdsk e: command, the following message may be displayed:

The type of the file system is FAT32.

Volume Serial Number is C408-2213

Errors found. CHKDSK cannot continue in read-only mode.



CAUSE
This behavior occurs because the FAT32 file system contains a backup copy of the boot sector. However, Chkdsk.exe does not attempt to use the backup FAT32 boot sector unless the primary boot sector is physically located in a bad sector and Chkdsk.exe receives an I/O error message while trying to read the volume. Chkdsk.exe does not try to use the backup copy because the primary copy is corrupted or contains invalid information.



RESOLUTION
If you have a corrupted primary boot sector, you can use the Dskprobe tool (Dskprobe.exe) to make repairs by copying the backup boot sector over the corrupted primary boot sector.

The primary boot sector is sector 0 of the logical drive. The backup FAT32 boot sector is located at sector 6 of the logical drive. While in byte view, read sector six of the logical drive and write it over sector zero of the logical drive.

Use the following steps to restore the backup FAT32 boot sector.

NOTE: To ensure the repair operation is successful, keep Dskprobe.exe in byte view throughout this procedure.  Extract the Dskprobe.exe from the Support\Tools\Support.cab file located on the Windows 2000 installation CD-ROM. Run Dskprobe.exe. On the Drives menu, click Logical Drive, and then double-click DriveLetter (where DriveLetter is the FAT32 volume that you want to repair). Click to clear the Read only check box, click set active, and then click OK. On the Sectors menu, click Read, and then change the default Starting sector value from 0 to 6 (do not change the Number of Sectors=1 value). This action reads the backup FAT32 boot sector. On the Sectors menu, click Write.</li> Verify that the active handle is still the logical drive letter of the volume being fixed, change the starting Sector to write data value from 6 to 0, and then click Write it. Click Yes to confirm you want to overwrite sector 0 on device DriveLetter.</li> Quit Dskprobe.exe and run Chkdsk again against the repaired volume using the following command:

chkdsk DriveLetter:

NOTE: Use the /f switch if the volume requires additional fixing.</li></ol>

<div class="status_section">

STATUS
Microsoft has confirmed this to be a problem in Microsoft Windows 2000.

<div class="moreinformation_section">

MORE INFORMATION
246146 Dskprobe.exe May Damage FAT32 Boot Sector

Additional query words: unreadable mbs corrupt

Keywords: kbbug kbenv kbpending KB247575

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