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Dskprobe.exe May Damage FAT32 Boot Sector

Article ID: 246146 - View products that this article applies to.

This article was previously published under Q246146

SYMPTOMS

Windows 2000 supports the FAT, FAT32, and NTFS file systems. If you use any version of the the Dskprobe.exe utility except the version that is included on the Windows 2000 CD-ROM or in the Microsoft Windows 2000 Resource Kit to view and then save a FAT32 boot sector, the associated FAT32 partition may become unreadable. When this occurs, the Windows 2000 Chkdsk tool reports that the volume contains errors, but does not fix them. For example:

chkdsk e:
The type of the file system is FAT32.
Volume Serial Number is C408-2213

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

chkdsk e: /f
The type of the file system is FAT32.
Volume Serial Number is C408-2213

chkdsk e:
The type of the file system is FAT32.
Volume Serial Number is C408-2213

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

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

247575

(http://support.microsoft.com/kb/247575/EN-US/ )

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

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CAUSE

The Dskprobe.exe utility is not FAT32-aware and can cause FAT32 boot sector damage if the following conditions are true:

After reading a FAT32 boot sector, you click FAT Boot Sector on the View menu.
You choose to save or write the FAT32 boot sector, even if you made no changes.

This problem occurs because Dskprobe changes some static values that are FAT boot sector-specific, but are used differently on FAT32 partitions.

The following text is the output of a GoodSector.dsk and BadSector.dsk boot sector compare:

C:\>comp
Name of first file to compare: GoodSector.dsk
Name of second file to compare: BadSector.dsk
Option:
Comparing GoodSector.dsk and BadSector.dsk...
Compare error at OFFSET 2B
file1 = 0
file2 = 20
Compare error at OFFSET 2C
file1 = 2
file2 = 20
Compare error at OFFSET 2D
file1 = 0
file2 = 20
Compare error at OFFSET 2E
file1 = 0
file2 = 20
Compare error at OFFSET 2F
file1 = 0
file2 = 20
Compare error at OFFSET 30
file1 = 1
file2 = 20
Compare error at OFFSET 31
file1 = 0
file2 = 20
Compare error at OFFSET 32
file1 = 6
file2 = 20
Compare error at OFFSET 33
file1 = 0
file2 = 20
Compare error at OFFSET 34
file1 = 0
file2 = 20
10 mismatches - ending compare

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RESOLUTION

The FAT32 file system contains a backup copy of the boot sector. You can use Dskprobe.exe to copy the backup copy over the corrupted boot sector. The primary boot sector is sector zero of the logical drive; the backup FAT32 boot sector is located at sector six of the logical drive. In Byte view, read sector six of the logical drive and without viewing it as a "FAT Boot Sector," write it over sector zero of the logical drive.

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

WARNING: For FAT32 partitions, do not view the boot sectors as a FAT boot sector from the View menu and then save it. Doing so corrupts it again. Instead, leave Dskprobe in the default mode of Byte view throughout the editing session.

Start Dskprobe.exe.
On the Drives menu, click Logical Drive, and then double-click the drive letter representing the FAT32 volume that needs to be repaired.
Click to clear the Read Only check box, click Set Active, and then click OK.
On the Sectors menu, click Read, change the Default Starting Sector value from 0 to 6, and leave the Number Of Sectors=1 value alone. This reads the backup FAT32 boot sector.
On the Sectors menu, click Write.
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 zero 0, and then click Write It. Click Yes to confirm that you want to overwrite sector 0 on the drive.
Quit the Dskprobe tool, and then run Chkdsk against the repaired volume:
chkdsk logical_drive_letter:
Use the /f switch if the drive requires additional fixing.

When you use Dskprobe on FAT32 volumes, do not view the boot sectors as a FAT boot sector from the View menu and then save it. Instead, leave Dskprobe.exe in Byte mode when you are viewing or making changes to FAT32 boot sectors.

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