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Beginners Guides: Diagnosing Bad Hard Drives
Beginners Guides: Diagnosing Bad Hard Drives - PCSTATS
Know... before your hard drive kicks the bucket, taking all your data with it. Clickity-click, time to defuse that dying hard disk!
Filed under: Beginners Guides Published:  Author: 
External Mfg. Website: PCSTATS May 01 2011   M. Dowler  
Home > Reviews > Beginners Guides > PCSTATS

What do bad sectors mean?

A bad sector is a sector of the disk to which data cannot be written. This may be due to a number of reasons, but to your operating system all that matters is that it can no longer use that portion of the disk. If the disk has yet to be used, or is being reformatted, bad sectors are not really an issue. All recent operating systems map a drive's bad sectors and avoid them while formatting it for use.

Modern hard drives are manufactured with 'spare' sectors which are only used to replace space lost due to bad sectors. This allows a drive to automatically compensate for any slight manufacturing defects which may have resulted in the drive having bad sectors 'out of the box.' When formatting a drive, bad sectors are detected and these 'spare' sectors are used to replace them as necessary.

Where bad sectors become an issue is when previously usable sectors become damaged due to disk error. Any data on these sectors is in danger of being corrupted or destroyed. The operating system has no way of automatically compensating for this loss, potentially leading to data corruption on a larger scale and system instability if the affected data was crucial.

Bad sectors can be created by software errors, or slight errors in the read/write heads which cause the data laid down on that particular sector to be completely illegible, and thus appear as bad to the operating system. This type of 'soft' bad sector can generally be fixed by completely erasing the disk (by writing every sector over with a pattern of zeroes).

Bad sectors created by a mechanical error have a tendency to breed more bad sectors quickly. Since the margin for error inside a working disk is so slim, any surface damage or debris created by a mechanical failure or 'head-crash' will quickly cause more damage as it interferes with the read/write heads. When formatted, a drive with 'hard' bad sectors like these will use the spare sectors to as much as possible replace the existing bad sectors as detailed above. Of course, if the bad sectors are still spreading due to loose particles or surface errors in the disk, the disk will still be unstable. At this point, the only option is to salvage as much data as possible from the drive before it dies completely.

Fortunately there are ways to fix or work around bad sectors on a disk.

Hard disk checking and repair methods

There are three main methods of testing and fixing the integrity of your drives and your data. We will look at some applications that perform these tests a little later in the guide.

Error checking is the process of scanning the files and folders present on your drive, searching for corrupt files and inconsistencies. For example, deleted files which the file system still contains entries for, or files which are referenced more than once. This can clean up basic file problems which might be causing data issues on your disk. If you constantly experience errors while performing error checking it could be a sign that your drive is dying, and bad sectors are proliferating. Error checking takes very little time to carry out.

A surface scan examines each sector of the disk in detail in order to identify and mark bad sectors. These areas of the disk can then be marked off-limits to the file system, and spare sectors used to replace them. Surface scans typically take a large amount of time to perform, but are the only non-destructive way to map out any bad sectors on your drive that have developed since you last formatted it.

SMART diagnostics test: A SMART test queries the internal SMART (Self-Monitoring, Analysis and Reporting Technology) information of your drive for its current status. This serves as a test of your drive's current physical well being. We'll get into the benefits of using SMART next, but first, what are the warning signs of a failing hard drive?

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Contents of Article: PCSTATS
 Pg 1.  Beginners Guides: Diagnosing Bad Hard Drives
 Pg 2.  How Hard Drives Can Fail
 Pg 3.  — What do bad sectors mean?
 Pg 4.  Warning signs to watch for
 Pg 5.  Hard disk diagnostic tools
 Pg 6.  Manufacturer Produced Hard Drive Utilities
 Pg 7.  HDD Diagnostic Software
 Pg 8.  Diagnostic Software con't
 Pg 9.  Fixing bad sectors - the last resort

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