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Thread: Questions regarding HDD spare sectoring

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    Amateur photographer Hans Voralberg's Avatar
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    Questions regarding HDD spare sectoring

    Spare sectoring, as far as i knew, is marking bad sector and tell the controller on the HDD to used another back-up sector when the head move to the bad ones, right ? And this is done in factory, to create new bad sector free HDD (as manufacture process is never perfect). And when in use, if any bad sectors aroused, zero-filling the HDD can do the same thing, remap the bad sectors to its back-up (that's what I read over at The PC Guide). But what I want to know is, is there really enough spare sectors, even for a few meg ?? Personally I don't think so, i've been zero-filling lots of bad HDD and yet all that don't seems to have any effect ??

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    I had a segate SCSI drive go bad once. Running a format from the SCSI card allowed me to zero and remap the drive, but at (if I recall correctly) about 10%, the format procudure quit with an error code.

    Segate told me the error meant I'd run out of, as you put it "back-up" sectors, and that the drive was done for.

    There are never THAT many bad sectors... unless the drive isn't worth recovering.
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    Amateur photographer Hans Voralberg's Avatar
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    Not quite got the idea of your last sentence Kez, (not a native speaker though).

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    Basically I'm tring to say the reason that there are only a few "back-up" sectors is that once a lot start appearing - the drive is quickly going to be become useless.
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    Amateur photographer Hans Voralberg's Avatar
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    Yup, got it. Thanks a lot.

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    please can someone explain to me why bad sectors should appear after the manufacturing process. I understand that during the manufacturing process, things are bound to go wrong to a certain degree - and therefore bad sectors occur.

    But i cant work out how they occur after. The magnetic heads have no contact with the spinning metal. I thought the only way something went wring with a hard drive was when the motor failed. How can a bit of metal with microscopic magnetic charge suddenly not work, it defies the laws of physics - things must become charged and discharged if a certain charge is focused upon them.

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    Amateur photographer Hans Voralberg's Avatar
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    Yeah, that's nice question from Timmy, never wonder why bad sectors develop while we're using them. Although personally after dropping a few drives on the floor due to my clumsiness, bad sectors did appeared

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    You platters are spinning at a rapid rate, the only thing keeping the heads from coming in contact with the platter is a smile cushion of air (smaller than a piece of dust!). If something gets in the hard drive (ie- a piece of dust) the heads could 'crash' and come in contact with the platter. This could cause some of the magnetic media to come off resulting in an unreadable sector. This usually isn't that big of a deal, but if enough magnetic 'flakes' (for lack of a better word) come off, a cycle starts. What happens is that those 'flakes' cause the head to contiunally crash, causing more 'flakes' to build up until you have a dead drive. Hope this helps.

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    Quote Originally Posted by Spritzup
    You platters are spinning at a rapid rate, the only thing keeping the heads from coming in contact with the platter is a smile cushion of air (smaller than a piece of dust!). If something gets in the hard drive (ie- a piece of dust) the heads could 'crash' and come in contact with the platter. This could cause some of the magnetic media to come off resulting in an unreadable sector. This usually isn't that big of a deal, but if enough magnetic 'flakes' (for lack of a better word) come off, a cycle starts. What happens is that those 'flakes' cause the head to contiunally crash, causing more 'flakes' to build up until you have a dead drive. Hope this helps.
    Thanks for the great reply, i can kind of understand it now. But how can 'flakes' develop if the drive is made in a vacum (no dust) environment? Do the flakes somehow develop from the spinning head and motor?

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    Is spelt 'Vacuum' and they arent. they are filled at manufacture with a super clean inert gas (most likely nitrogen or maybe just clean air). A vacuum would require serious structural work on the drive to ensure it could cope with the strain.

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    Oh ok. Hmm yea now thinking about it a vacuum would be a bit hard to create. So the dust just finds its way in due to the stickers being hit/worn or something I suppose.
    (the stickers that say warranty void if removed)

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    They are built in a clean room with little to no dust. On top of that the Hard Drive has a built in filter to keep dust out. But with the space between head and the platter being only around a micron thick, it doesn't take much to throw it off. Also the aforementioned filter will pick up a bit of the magnetic flakes.

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