Chkdsk.exe is the command-line interface for the CHKDSK program, which verifies the logical integrity of a file system. If CHKDSK encounters logical inconsistencies in file system data, CHKDSK performs actions that repair the file system data (assuming that the data is not in read-only mode).

The /C and /I switches are valid only for a drive that is formatted in the NTFS file system. Each of the new switches directs the CHKDSK routine to bypass certain actions that CHKDSK would otherwise take to validate the integrity of NTFS data structures.

…

Introducing the /C and /I switches The /C switch The /C switch directs CHKDSK to skip the checks that detect cycles in the directory structure. Cycles are a very rare form of corruption in which a subdirectory has itself for an "ancestor."

Using the /C switch can speed up CHKDSK by about 1 to 2 percent, but using this switch can also leave directory "loops" on an NTFS volume. Such loops might be inaccessible from the rest of the directory tree, and some files might be orphaned in the sense that Win32 programs, including backup programs, cannot see the files. The /I switch The /I switch directs CHKDSK to skip the checks that compare directory entries to their corresponding file record segments. With this switch in effect, directory entries are still checked for internal consistency, but the directory entries are not necessarily consistent with the data that is stored in the corresponding file record segments.

How much time you will save by using the /I switch is difficult to predict. Typically, the /I switch lowers CHKDSK times by 50 to 70 percent, depending on factors such as the ratio of files to directories and the speed of disk I/O relative to CPU speed.

Using the /I switch has these limitations:

* You may have directory entries that refer to incorrect file record segments. In this case, any program that tries to use such an entry will encounter errors.
* You may have file record segments that no directory entry references (another way that orphaned files occur). A file that is actually intact, as represented by the file record segment, may be invisible to all Win32 programs, including backup programs.

The value of the /C and /I switches When disk corruption is detected on a volume, there are three basic options for response.

The first option is to take no action. On a mission-critical server that is expected to be online 24 hours a day, this is often the choice of necessity. The drawback is that relatively minor corruption can snowball into major corruption. Therefore, consider this option only if keeping the server online is more important than guarding the integrity of the data that is stored on the corrupted volume. All data on the corrupted volume should be considered "at risk" until you run CHKDSK. The second option is to run a full CHKDSK operation to repair all file system data and restore all of the user data that can be recovered by means of an automated process. However, running a full CHKDSK operation can cost you several hours of downtime for a mission-critical server at an inopportune time. Your third option is to run an abbreviated CHKDSK operation by using one or both of the /C and /I switches, to repair the kinds of corruption that can snowball into bigger problems in much less time than a full CHKDSK requires.

Note however that running an abbreviated CHKDSK does not repair all of the corruption that might exist. You still need to run a full CHKDSK at some future time to guarantee that all recoverable data has in fact been recovered.

Note also that NTFS does not guarantee the integrity of user data after an instance of disk corruption, even if you immediately run a full CHKDSK operation. There might be files that CHKDSK cannot recover, and files that CHKDSK does recover might still be internally corrupted. It remains vitally important that you protect mission-critical data by performing periodic backups or by using some other robust method of data recovery.

[http://support.microsoft.com/?id=314835]