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#1
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When does an HDD replace bad sectors?
I understand that a modern HDD has many spare sectors which it automatically
substitues for bad sectors until it runs out of spares, and that a bad sector showing up in the OS is a sign that the drive has aged too much to be reliable. But when does the substitution take place? I expect that, for one, it happens during a full format. Does it also happen quietly in the background on the fly during normal use under an OS? |
#2
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When does an HDD replace bad sectors?
pimpom wrote:
I understand that a modern HDD has many spare sectors which it automatically substitues for bad sectors until it runs out of spares, and that a bad sector showing up in the OS is a sign that the drive has aged too much to be reliable. But when does the substitution take place? I expect that, for one, it happens during a full format. Does it also happen quietly in the background on the fly during normal use under an OS? A write to the sector, sounds like an excellent time to handle suspect sectors. SMART has a couple statistics Reallocated_Sector_Count Current_Pending_Sector A reallocated sector, is one that has been replaced. There are only so many spares in a given locality to a bad sector, so eventually a sector may not be repairable. For example, it wouldn't make sense for sector 0, to be used as a replacement for sector 10000000. The "Current_Pending", suggests that during a read attempt, a sector got marked as being dodgy. The drive can't do anything about it, until a write is attempted. On the write, the controller knows what the new data is supposed to be, so it is in a better situation to do a potential reallocation. The Current_Pending value gets decremented by one, and maybe the Reallocated gets incremented by one. If the sector tested as OK, it might not get reallocated. I tried looking for a description with more algorithmic details, but couldn't find anything worth repeating. You could look at PDF page 22 here. It is purposefully vague, because being a spec handed to customers, they don't want to commit to anything. http://www.hitachigst.com/tech/techlib.nsf/techdocs/1AFE1C40F435EEB0862572F10049BAFD/$file/5K250_spec.pdf Paul |
#3
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When does an HDD replace bad sectors?
On Thu, 21 May 2009 11:50:13 +0530, "pimpom"
wrote: I understand that a modern HDD has many spare sectors which it automatically substitues for bad sectors until it runs out of spares, and that a bad sector showing up in the OS is a sign that the drive has aged too much to be reliable. But when does the substitution take place? I expect that, for one, it happens during a full format. Does it also happen quietly in the background on the fly during normal use under an OS? To fix errors in an HDD you need to run utilities like CHKDSK, short for "Check Disk". There are other softwares useful, like SpinRite. Anyway, you can't save a physically broken HDD. -- http://ManuelMarino.com (Arts, Music) http://NewOnlineShopping.net (Clothing, Gifts) http://TechGamesBlog.com (Technology, Games) |
#4
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When does an HDD replace bad sectors?
In message Manuel
was claimed to have wrote: On Thu, 21 May 2009 11:50:13 +0530, "pimpom" wrote: I understand that a modern HDD has many spare sectors which it automatically substitues for bad sectors until it runs out of spares, and that a bad sector showing up in the OS is a sign that the drive has aged too much to be reliable. But when does the substitution take place? I expect that, for one, it happens during a full format. Does it also happen quietly in the background on the fly during normal use under an OS? To fix errors in an HDD you need to run utilities like CHKDSK, short for "Check Disk". That will check filesystem integrity and/or help to deal with bad sectors in software. However, most hard drives have the ability to remap bad sectors, and will do so whenever there is a repeated write failure on a given sector. |
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