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[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting Specific Components | Troubleshooting Hard Disk Drives | Errors ]

My hard disk has bad sectors or is developing bad sectors over time

Explanation: The hard disk (through disk checking utilities) is reporting that one or more of its sectors are bad. This may be on a new drive, or there may be bad sectors showing up on a drive that has been in a system for a while.

Diagnosis: Unsurprisingly, bad sectors are generally a real problem with a hard disk and usually imply a legitimate problem with the hard disk itself. There are configuration problems that may be responsible, and these are usually resolved pretty easily, however the usual problem is the drive itself. Bear in mind that IDE/ATA and SCSI drives, at least all of the ones produced in the last five years or so, use a technique called remapping or spare sectoring to hide bad sectors detected on the drive at the factory. A new hard disk should have zero bad sectors on it. An older drive may "grow" a bad sector or two now and again, however in many cases this is a harbinger of impending disaster with the disk. Take it as the warning sign it is.

Recommendation: The steps below discuss possible problems that can lead to a bad sector showing up. In addition to trying to eliminate the cause, you also should contact your hard disk manufacturer's technical support department (phone or web site) and inquire about a utility to remap the bad sector so it is hidden and replaced with one of the spares on the disk (fixing the cause of the bad sectors is important but that doesn't get rid of the ones that are already there in some cases):

  • As soon as you see any bad sectors show up on a disk that contains data, make sure you back up the disk immediately, or you risk possible loss of your data. I would avoid making any significant changes to the software setup on the drive, or adding any new data to it, until you get the situation resolved.
  • Make sure that you have not set the hard disk timing (PIO mode) too high for the drive. You may want to try reducing the timing and seeing if this resolves the problem. Make sure that if your system does not support independent device timing, that you do not have the PIO mode set for what is optimal for the faster of two devices, but too fast for the slower one.
  • Make sure that you are not using an IDE cable that is too long. The specified maximum is 18 inches, but some drives need them to be even shorter than that to work properly. Try replacing the cable with a shorter one, if possible.
  • If you are getting bad sectors on more than one disk in the system, or even after replacing the disk, then the problem lies somewhere other than the disk, most likely. Suspect incorrect BIOS settings, and I would troubleshoot the motherboard as well. It could even be bad power from the power supply.
  • Some hard disks have firmware problems. In this case the manufacturer may make a firmware upgrade available for the disk; this is like a flash BIOS upgrade for your hard disk (except it is easier to install and is used only for fixing bugs). Check your manufacturer's web site for more information on this possibility. I know for example that this has happened with some of Western Digital's Caviar series hard disks and in many cases the firmware upgrade resolved the problem nicely.
  • Try to make sure that you have eliminated any of the possible configuration gotchas that can lead to problems with bad sectors. If you do and are still getting more bad sectors showing up, the drive should be treated as imminently failing and you should contact your manufacturer's or system vendor's technical support department. If the drive is new or the system is still under warranty, insist on a replacement drive. See here for more. There is no reason for a new hard disk to have bad sectors on it, period. Don't let them try to convince you otherwise.
  • If you have a drive out of warranty that gets one or two bad sectors, then if you feel comfortable with the drive, map out the bad sectors and continue using it. In some cases, there is just one weak area on the disk, and the rest of it will continue to be quite usable for some time. However, if the number of bad sectors is large or is increasing in time, look out, because the chances of the drive failing outright become much higher when this happens.
  • On very old drives--meaning before IDE, the older drives from the mid-80s that used stepper motors--there is a phenomenon called "Monday morning blues" that can result in bad sectors showing up on hard disks. This occurs especially when the hard disks are cold, after being off overnight or over the weekend (thus the name). These stepper motor drives cannot compensate for thermal expansion of the disk platters and may not be able to read the tracks on the drive until the disk has warmed up. Waiting a half-hour may see the problem go away, but in the long run the disk will need to be low-level formatted again. (None of this applies to modern IDE or SCSI hard disks).

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