Windows 7

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Checking Disks for Errors

Errors in disk media and in the file system can cause a wide range of Windows problems, ranging from an inability to open or save files to blue-screen errors and widespread data corruption. Windows is capable of recovering automatically from many disk errors, especially on drives formatted with NTFS.

To perform a thorough inspection for errors, you can manually run the Windows Check Disk utility, Chkdsk.exe. Two versions of this utility are available-a graphical version that performs basic disk-checking functions, and a command-line version that provides a much more extensive set of customization options.

To check for errors on a local disk, follow these steps:

1. Open Computer, right-click the icon belonging to the drive you want to check, and then choose Properties from the shortcut menu.
2. On the Tools tab, click Check Now. (If you're using a standard account, you'll need to supply credentials for an account in the Administrators group to execute this utility.
3. In the Check Disk dialog box, shown next, select from the following options:
   • Automatically Fix File System Errors:
     This option, which is enabled by default, configures Windows to automatically repair any errors it detects in the file system. If this option is not selected, Check Disk reports any errors it finds but does not correct them. This option is the equivalent of running the Chkdsk command with the /F switch, as described later in this section.
   • Scan For And Attempt Recovery Of Bad Sectors:
     Select this option to perform an exhaustive check of the entire disk, locate bad sectors, and recover readable information stored in defective locations. Note that selecting this option automatically repairs file system errors as well, even if the previous option is cleared. This option is the equivalent of running the Chkdsk command with the /R switch.
   If you simply want to see a report of file system errors without making any changes to disk structures, leave both boxes unselected.
4. Click Start to begin the disk-checking process. The green progress bar provides feedback as the error-checking tool goes through several phases.
   If you select the Automatically Fix File System Errors option on a drive that currently has open files, Windows is unable to run the utility immediately.

Click Schedule Disk Check to configure Windows startup so that the disk check utility runs the next time the computer is started. The disk check occurs early in the startup sequence, before Windows shifts into graphical mode; during this period, your computer is not available for you to perform any other tasks. When your computer starts, Windows notifies you that it's about to perform a scheduled disk check; by default, you have 10 seconds to cancel the operation and boot normally instead.

After Check Disk completes its operation, it reports its results. If the disk check turns up no errors, you see a Disk Check Complete dialog box. If Check Disk uncovers any errors, it writes a message to the System event log and displays a dialog box listing the errors it found and the repairs it made.

Although Check Disk is a useful tool and sometimes a lifesaver, it can cause you headaches if used without some planning. After it has started, the Check Disk operation cannot be stopped except by pressing your computer's power switch. On large drives (hundreds of gigabytes or more), the full disk check can take hours or even days to complete.

Check Disk runs automatically after an abnormal shutdown only if a specific bit in the registry is set, indicating that the file system is "dirty"-that is, that some pieces of data were not properly written to the disk when the system was shut down. If the file system wasn't doing anything when the system shut down, the dirty bit will not be set. Because NTFS volumes keep a journal of all disk activities, they are able to recover and remain clean even if you shut down in the middle of a disk write. Check Disk is most likely to run automatically at startup only on FAT32 volumes, after an unexpected shutdown.

Cancel checks with Chkntfs
Two additional and well-hidden Windows commands are crucial to the operation of the Check Disk utility. The first of these, Autochk.exe, runs automatically any time you specify that you want to schedule a disk check to run at startup; it cannot be run interactively. The second, Chkntfs.exe, is especially useful if you change your mind and decide you want to cancel a scheduled check. At a command prompt, type chkntfs /x d: (where d is replaced by a drive letter) to exclude the drive specified. Chkntfs has another nifty trick: it can tell you whether a disk is dirty. At a command prompt, simply type chkntfs d:.

The command-line version of Check Disk gives you considerably more options. It also allows you to set up regular disk-checking operations using the Task Scheduler. To run this command in its simplest form, open a Command Prompt window using the Run As Administrator option, and then type chkdsk at the prompt. This command runs Chkdsk in read-only mode, displaying the status of the current drive but not making any changes. If you add a drive letter after the command (chkdsk d:, for instance), the report applies to that drive. You can use any combination of the following switches at the end of the command line to modify its operation:

• /F
  Instructs Chkdsk to fix any errors it detects. This is the most commonly used switch. The disk must be locked. If Chkdsk cannot lock the drive, it offers either to check the drive the next time you restart the computer or to dismount the volume you want to check before proceeding. Dismounting is a drastic step; it invalidates all current file handles on the affected volume and can result in loss of data. You should decline the offer. When you do, Chkdsk will make you a second offer-to check the disk the next time you restart your system. You should accept this option. (If you're trying to check the system drive, the only option you're given is to schedule a check at the next startup.)
• /V
  On FAT32 volumes, /V displays verbose output, listing the name of every file in every directory as the disk check proceeds. On NTFS volumes, this switch displays cleanup messages (if any).
• /R
  Identifies bad sectors, and recovers information from those sectors if possible. The disk must be locked. Be aware that this is a time-consuming and uninterruptible process.

The following switches are valid only on NTFS volumes:

• /I
  Performs a simpler check of index entries (stage 2 in the Chkdsk process), reducing the amount of time required.
• /C
  Skips the checking of cycles within the folder structure, reducing the amount of time required.
• /X
  Forces the volume to dismount, if necessary, and invalidates all open file handles. This option is intended for server administrators. Because of the potential for data loss, it should be avoided.
• /L[:size]
  Changes the size of the file that logs NTFS transactions. If you omit the size parameter, this switch displays the current size. This option is intended for server administrators. Because of the potential for data loss, it also should be avoided in normal use.
• /B
  Reevaluates bad clusters.

Troubleshooting

When you run Chkdsk in the Windows Recovery Environment, some options are not available.

The Chkdsk command used when you boot to the Windows Recovery Environment is not the same as the one used within a full Windows session. Only two switches are available for this version:

• /P Performs an exhaustive check of the current disk
• /R Repairs damage on the current disk

If your system is able to boot to Windows either normally or in Safe Mode and you suspect that you have disk errors, you should use the full Chkdsk command.