about CHKDSK
Chkdsk is a command-line utility that verifies the logical integrity of a file system on Windows 2000. NTFS, which maintains the integrity of all NTFS volumes, automatically runs Chkdsk the first time that Windows 2000 mounts an NTFS volume after the computer is restarted following a failure. You can also manually run Chkdsk or schedule Chkdsk to be run if you suspect there may be file system corruption.
Chkdsk examines all the metadata on a volume, compares it to the transaction logs that are maintained by NTFS, and if it finds logical inconsistencies, it takes actions to repair file system data. Metadata is “data about data.” It is the file system overhead, so to speak, that NTFS uses to keep track of everything about all the files on the volume. For example, metadata tells NTFS which allocation units make up the data for a particular file, which allocation units are free, and which allocation units contain bad sectors.
If Chkdsk runs at a time other than during the startup process, the code that actually performs the verification resides in utility dynamic-link libraries (DLLs), such as Untfs.dll and Ufat.dll. The verification routines that Chkdsk runs are the same ones that are run when Windows Explorer or Disk Administrator verifies a volume through its graphical user interface (GUI). If Chkdsk runs during the startup process, the binary module that contains the verification code is Autochk.exe.
Autochk is an integrated Windows 2000 command-line utility that runs early enough in the system startup process that it does not have the benefit of virtual memory or other Win32® application programming interface (API) services. Autochk generates the same kind of textual output that Chkdsk does, except that in addition to displaying this output on the screen during the startup process, Autochk also logs an event to the Application event log for the system. This event contains as much textual output as can fit into the event log's data buffer.
Because Autochk and the verification code in the utility DLLs that are used by Chkdsk are based on the same source code, this white paper will sometimes refer to Autochk and Chkdsk collectively as Chkdsk.
After the release of Microsoft Windows NT® 4.0 Service Pack 4 (SP4) and Windows 2000, Microsoft added two new command-line switches, /i and /c, to Chkdsk. These options are only valid when the destination drive has the NTFS file format. Each option directs Chkdsk to bypass certain actions, which reduces the time it takes Chkdsk to run. The /c option directs Chkdsk to skip the checking of cycles in the folder structure, and the /i option directs Chkdsk to perform a less vigorous check of index entries.
These command-line switches are intended for users with exceptionally large volumes who require flexibility in managing system downtime. Because the use of the /c and /i options can result in a volume remaining corrupted after Chkdsk has completed, it is a good idea to use these options only in situations in which system downtime must be kept to an absolute minimum.
To understand when it is appropriate to use these command-line switches, it is important to understand some of the internal NTFS data structures, the kinds of corruption that can happen, what actions Chkdsk takes when it verifies a volume, and what the potential consequences are if you circumvent the typical Chkdsk verification steps.
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