Data Recovery: Data Loss and Drive Failures

Scan Disk, Bad Sectors, and CHK Files, Oh My!

Once in a while, machines will boot up and scandisk will be right there to greet you. Ok, this isn’t so bad. Maybe the shutdown procedure wasn’t fully completed or perhaps you just experienced a crash. This situation takes a turn for the worse when scandisk starts scanning for “bad sectors” or “bad clusters”. These bad sectors are areas on the platters of your hard drive that have become problematic physically. Dust on the platters, worn spots created by some component of the hard drive coming into contact with the platters, a misaligned drive head, or just through normal wear and tear can all be causes of “bad sectors”. To put it simply, it is damage somewhere on the platter, and these clusters can no longer hold data reliably. What scandisk does is try to recover the cluster, and move the data located there to another place on the drive that is undamaged. In spite of this, scandisk does nothing to prevent any more bad sectors from appearing, and nor does halting the scanning procedure.

Scanning the drive can be a time consuming process. Let it do its thing and come back every 20 minutes to half hour to check on its progress and to clear any messages that may alert you to the status of any bad sectors, or errors that may need your confirmation to be repaired.

If there are only a couple of bad sectors, it’s not much to worry about. The time to start worrying is when they start appearing all over the place. Usually the more you have, the more you will get. Meaning, it’s like a ripple effect. Once the number of bad sectors starts to increase, it will keep increasing until the drive becomes pretty much useless. Sometimes you can regain some of those sectors by zero filling the drive, formatting and finally running a through scandisk to check and mark bad sectors, but it’s really not worth the hassle. The process will most likely repeat itself. In the case of bad sectors, it only gets worse. So, grab what data you can, and get the drive replaced. If it is still under warranty, get it replaced through the manufacturer. If not, you are out of luck, and will have to go out and put down some cash for another hard drive.

So, what does scandisk/chkdisk do if it’s not scanning for bad sectors? Well, any time operating system crashes or the system is not shut down correctly, scandisk/chkdisk is run at startup. It is a good idea just to let it do its thing. Any files that were open and not closed properly when the computer was shut down incorrectly will be checked and possibly be repaired. If it is not repaired, then it is saved as a CHK file. Part of closing process is to write the file location information in the right places on the drive. Without it, the operating system may not be able find all the parts of the file, especially if the hard drive is heavily fragmented. When scandisk/chkdisk is run, these the parts are identified as “lost file fragments” and converted into *.chk files to correct the error. If you were working on something important just before a crash that looks like was lost when you boot back up, you might want to try to recover the data from any *.chk files that exist (Check out CHK-Mate, listed earlier).

The follow-up question seems to be is that if these files seem to be so important, can they be deleted? If you need to delete them, then run a disk defragmenter first. That way, the data is rearranged on the drive so your operating system knows where everything again, and the *.chk files probably aren’t needed. With file locations, you never know. Delete away at your discretion.