Chkdsk examines disk space and use for the NTFS and FAT file systems. Information
specific to each file system is provided in a status report. The status report
shows errors found in the file system.
If errors exist on the disk, chkdsk alerts you with a message and corrects the errors if the /f switch was used. Chkdsk must be able to lock the drive to correct errors. If errors are found but the
drive cannot be locked, an error message is displayed. If you run chkdsk without the /f switch on an active partition, it may report spurious errors,
since it will not lock the volume.
You should use chkdsk occasionally on each disk to check for errors.
Checking a locked drive at reboot
Files cannot be open on a drive when chkdsk corrects disk errors it finds. If files are open chkdsk offers to check the drive the next time the computer reboots. If you choose
to check the drive the next time the computer reboots, the drive will be checked
and errors will be corrected automatically at reboot. If the drive partition
is a boot partition, upon completion it will reboot the computer.
Checking a FAT disk
Windows NT displays chkdsk status reports for a FAT disk in the following format:
Volume Serial Number is B1AF-AFBF
72214528 bytes total disk space
73728 bytes in 3 hidden files
30720 bytes in 12 directories
11493376 bytes in 386 user files
61440 bytes in bad sectors
60555264 bytes available on disk
2048 bytes in each allocation unit
35261 total allocation units on disk
29568 available allocation units on disk
Checking an NTFS disk
Windows NT displays chkdsk status reports for an NTFS disk in the following format:
The type of the file system is NTFS.
CHKDSK is verifying files...
File verification completed.
CHKDSK is verifying indexes...
Index verification completed.
CHKDSK is verifying security descriptors...
Security descriptor verification completed.
12372 kilobytes total disk space.
3 kilobytes in 1 user files.
2 kilobytes in 1 indexes.
4217 kilobytes in use by the system.
8150 kilobytes available on disk.
512 bytes in each allocation unit.
24745 total allocation units on disk.
16301 allocation units available on disk.
Fixing disk errors
The chkdsk command corrects disk errors only if you specify the /f switch. Since repairs usually change a disk's file allocation table and
sometimes cause a loss of data, chkdsk first prompts you with a confirmation message similar to the following:
10 lost allocation units found in 3 chains.
Convert lost chains to files?
If you press Y, Windows NT saves each lost chain in the root directory as a file with a name
in the format FILEnnnn.CHK. When chkdsk finishes, you can check these files to see if they contain any data you need.
If you press N, Windows NT fixes the disk but does not save the contents of the
lost allocation units.
If you do not use the /f switch, chkdsk alerts you with a message if a file needs to be fixed but does not fix the
If you use chkdsk /f on a very large disk (for example, 70 GB) or a disk with a very large number
of files (millions), chkdsk may take a long time (perhaps days) to complete. The computer will not be
available during this time, as chkdsk does not relinquish control until it is done.
Using chkdsk with open files
If you specify the /f switch, chkdsk shows an error if open files are found on the disk. If you do not specify the /f switch and open files exist, chkdsk might report lost allocation units on the disk. This could happen if open
files have not yet been recorded in the file allocation table. If chkdsk reports the loss of a large number of allocation units, consider repairing
Physical disk errors
Use the /r switch to find physical disk errors in the file system. For information about
recovering physically damaged files, see the recover command.
Bad disk sectors
Bad sectors reported by chkdsk were marked as "bad" when your disk was first prepared for operation. They
pose no danger.