Windows Explored

Everyday Windows Desktop Support, Advanced Troubleshooting & Other OS Tidbits

CRC & Bad Blocks

Posted by William Diaz on December 3, 2010

Its actually refreshing when I come across a problem that does not always manifest itself as  GUI error in Windows, or even a software problem for that matter. If, when trying to boot into Window, it fails to load in a timely manner or not load at all, try starting in SafeMode (F8). You should being able to see which system files are being loaded and, in cases where the file system and hard disk where it resides are having problems. you may get lucky (well, lucky in the sense that you can decipher what may be happening). For example, in the case of a laptop I was asked to diagnose it would hang at : “Loaded: \Windows\System32\drivers\crcdisk.sys

The loading phase of Windows would remain stuck here for upwards of 10 minutes or longer.
When Windows is stuck at crcdisk.sys, you can be certain that you are dealing with some kind of physical or logical defect, most often bad blocks on the hard disk. Physical defects like bad blocks on the disk are (magnetic) and cannot be corrected. If you don’t already know, CRC stands for cyclic redundancy check and (if you have been lucky enough to boot into Windows) you can see these reported as errors with a source as disk in the Windows Event Viewer:

Depending on the areas of disk that are affected, you may or may not be able to boot into Windows or performance may just stagger to a complete stop. To mitigate this, there is a simple thing you can do to mark these sectors as bad and try to recover data: run chkdsk.
The idea behind chkdsk (and any other disk repair utility) is to update the sector map table on the disk and mark the sector as bad so that it is no longer used going forward.

Chkdsk can be set to run from within in Windows by right-clicking the hard disk > Properties > Tools > Check Now under Error Checking > Reboot. In the event you cannot get into Windows, then boot in Safe Mode with Command Prompt and run chkdsk /f /r (see links below for all switches).

In this particular case, I left it running, stepped away for the better part of a day, but unfortunately the chkdsk had only progressed 12% I decided that there was too much damage to the disk and didn’t bother trying to progress any further. Alternatively, I opted to recover data by copying personal files and folders via the command prompt to a USB drive and later just by attaching the drive to an external enclosure and using Explorer since the copy process would fail often and leave it difficult for me to remember where it left.

If problems persist after completing chkdsk, the drive should be replaced ASAP. For details on using chkdsk, see this Microsoft KB article: or Technet


2 Responses to “CRC & Bad Blocks”

  1. Which process is easy to fix chkdsk errors .. ?? GUI OR CMD line .. ??

    • If the problem is with the disk where the OS is and you cannot get into the OS, as was the case here, then you have no choice but to use the command line, which is easy enough to run. You can also remove the drive, plug in into an enclosure and then into another system and run a chkdsk from Windows using the GUI. In fact, if you plug the problem disk into a Windows 7 system (havnt tried on in Vista), it will detect errors and offer to run a chkdsk from the GUI.

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