Hard drives and Bad Sectors

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Hard drives and Bad Sectors

Postby ~PJ~ » Fri Feb 03, 2006 9:27 am

Thought this article might be of use;

Bad Sectors

Explains it all quite well.

And more;

Myths
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Let there be respect for the earth,
Peace for its people,
Love in our lives,
Delight in the good,
Forgiveness for past wrongs,
And from now on a new start.
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Postby Karlsweldt » Sat Feb 04, 2006 7:07 am

Great references, ~PJ~.
The magnetic coating on the platter is very thin.. measured in atoms thick. If the surface is scratched in any way, or the coating flakes off, then that sector is not able to be written to or read from properly. The maintenance programs offered by the hdd manufacturer may be able to enter a permanent marker in the boot sector, to ignore that specific sector.. and it will not show in the normal access of the hdd. Older drives had a table (chart, map) of bad sectors hand-written so you knew which sectors were bad from the get-go. Today's drives are much better in quality than those of only a few years ago. There is no bad sector table listed on today's drives.

One caveat to remember today, as with older hard drives.. don't turn them against their spin axis rapidly, when operating. The air slip-stream beneath the heads may vanish momentarily.. causing head-to-platter contact, which may be the end of the drive! If you follow the spin axis when turning them, no harm is done. Same as with a gyroscope.
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Postby rogue_tomato » Mon Mar 06, 2006 10:57 pm

Nice links ~PJ :wink: ~, very informative. I especially liked the "myths" link... and I learned something to boot! I didn't know that a low level format can potentially repair a bad sector on a hd... I thought that once you have discovered a bad sector, it will remain a bad sector for the lifetime of the hd. Ah well, you learn new things everyday :wink:
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Postby ~PJ~ » Tue Mar 07, 2006 6:22 am

rogue_tomato wrote:Nice links ~PJ :wink: ~, very informative. I especially liked the "myths" link... and I learned something to boot! I didn't know that a low level format can potentially repair a bad sector on a hd... I thought that once you have discovered a bad sector, it will remain a bad sector for the lifetime of the hd. Ah well, you learn new things everyday :wink:


Unfortunately, that's not quite the case;

True, low level formatting can replace bad sectors with good sectors on the spare tracks that are part of every hard disk.

However, performance suffers because the heads have to seek to the spare tracks. In addition, there are only a limited number of spare sectors available on any hard disk.

Finally, bad sectors are a sign that something is wrong with the hard disk. Even if it was due to a single head crash, that traumatic event would have created debris within the platter compartment and a damaged head. The debris can gradually cause scratches and erosions on other parts of the platter while a damaged head will not be aerodynamically stable and will be more likely to crash in the future.

In other words, if you have critical data, it would be a smart thing to back up your data and replace the hard disk when you start detecting bad sectors. The hard disk may go on for a long time without more bad sectors appearing but the risk of it dying is real and should not be ignored.


It's not repairing the bad sectors but using spare sectors instead.
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Let there be respect for the earth,
Peace for its people,
Love in our lives,
Delight in the good,
Forgiveness for past wrongs,
And from now on a new start.
~PJ~
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