How to Fix a Bad Cluster on a Hard Drive

By Brian Nelson

In most cases, lost clusters are nothing more than an annoyance. Fixing them is a relatively straightforward process, though it can seem scary. The most important point it that a full scan can take a very long time on a big hard drive.

Using CHKDSK to Fix Your Hard Drive Issues

Step 1

Understand your problem. In a Windows-based file system, a cluster is a block of storage space that is not listed as free, but is not assigned to any file, either. In other words, the file system has marked the cluster to not be overwritten, but it doesn't know why. This does not necessarily indicate any problems with the hard drive itself. Usually, lost or bad clusters are the result of improper program terminations, like those due to power loss or shutting off a computer without closing the applications first.

Step 2

Open a command prompt or DOS prompt. Depending on which version of Windows you are using, there are multiple ways to run the CHKDSK utility. The method that works across most versions is to run it via the command line.

Step 3

Type "chkdsk /r" in your command prompt window. This tells the computer to run the CHKDSK utility and to repair any errors it finds. Your may need to reboot your computer to run the chkdsk utility.

Step 4

Wait for the utility to finish. Unless you begin seeing errors on the screen right away, it is probably in your best interest to go do something else while your computer checks the drive. The process can take hours, so there is not need to sit and stare at the screen.

Step 5

Reboot. After the utility has finished, reboot your system to start the operating system normally. Your lost clusters will be saved as files named with the convention: file####.chkThe data in such files is usually worthless. However, you may be able to analyze the files and recover some data if it is critical.

Tips & Warnings

  • Most disk defragmentation utilities fix lost clusters as part of the defragmentation process; however, they may not save the data.
  • You may see references to using the chkdsk /f command. The chkdsk /r command includes everything that the chkdsk /f does, so there is no need to run with /f after using /r.
  • Do not confuse lost clusters with bad sectors. Bad sectors usually indicate a hard drive that is beginning to fail.