Q: How do I remove a hard disk bad sector? (via Quora)
A: Try chkdsk (Windows) or fsck (Linux); both can detect and repair some kinds of damage to a hard drive. But have a care: Although some software can restore some bad sectors to service, it may be best not to!
Tools like fsck and chkdsk mostly correct “soft” errors — problems caused by programmatic malfunctions that mess up the disk’s logical (but not physical) structure. Errors of this sort are easy to fix, and usually don’t signify trouble with the actual hard drive itself.
But “hard” errors arise from physical, mechanical problems with the disk. Most hard drives have built-in mechanisms to take irreparably-damaged sectors out of service, and to re-map those locations to spare sectors included for that purpose in the OEM setup. (This usually happens silently and without fanfare; with no user notification or interaction at all.) Most newer drives are designed to allow for a certain number of errors/recoveries/relocations. As long as the total error count stays below the design threshold set by the manufacturer, all is well.
If the hard drive itself hasn’t detected and removed a bad sector from service, a tool like chkdsk may be able to detect the problem and mark the sector as unusable. That’s all fine and good; the unreliable sector will no longer be used to store data.
But some disk-repair software may force marginally bad sectors back into use. If the sector was taken out of service due to physical damage, the underlying damage may still be there. That means that sector’s data is at risk, even if fsck or chkdsk is temporarily happy. I don’t recommend trying to restore bad sectors to use.
Here’s a good rule of thumb: If a drive is experiencing any serious, frequent, or repeated disk errors for any reason, it’s a cry for help! You should immediately take three steps:
1) Backup your data ASAP to a safe alternative location (not on the same hard drive!).
2) Run a S.M.A.R.T. (“Self-Monitoring Analysis And Reporting Technology”) diagnostic tool to see what’s going on (examples for Linux; and for Windows). The SMART tool will tell you the frequency and severity of the disk errors you are experiencing, and even predict how much life your drive has left!
Figure 1 shows a SMART readout for a healthy hard drive on my main PC. Note the right-hand column: Many newer drives include this “TEC date” prediction (“Threshold Exceeded Condition”) in their SMART output — that’s how long the software thinks the drive has before the errors accumulate to the point of danger to your data. The TEC column for my drive shows N/A (not available) because — after almost 7,000 hours of operation with 0 read errors, and 0 relocated sectors — there’s no sign of failure at all, and thus no way for the software to extrapolate a TEC date. That’s good!
3) If your SMART monitor shows an impending TEC date, or if the drive is generating a significant number of errors (especially hard errors that signify physical damage and/or require relocation of the sector’s data), then that drive is near the end of its useful life and should no longer be trusted.
It’s time to buy a new hard drive!
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