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Bad blocks can be caused by hardware problems and may not be formatted out
Authored by: S Barman on Mar 09, '06 08:05:00AM

Rob: The reason why a format of the hard disk would not work is that if the disk's bad block is because of a physical defect, formatting will not fix the problem. This is a hardware issue that can only be fixed by changing the drive.

I have a 4G (U2) iPod and have not seen problems. But a friend who has a 3G iPod has had several bad blocks show up on his drive. It may be the age or quality of the drive. It can also be that the drive was bumped during use and the head became too close or even tapped the disk. If the head came too close, it could have also overwritten the servo information, which also makes the blocks useless and not able to format.

The bottom line... it's a hardware thing!

Good luck!



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Bad blocks can be caused by hardware problems and may not be formatted out
Authored by: alblue on Mar 09, '06 09:44:46AM

Bad blocks are caused by hardware faults, but that doesn't mean that they're only fixable by hardware means. All hard drives have bad blocks; most operating systems work around bad blocks by having a list of known-bad-blocks that they don't attempt to write on. When you do a low-level format of a disk (e.g. using the 'zero all blocks' of Apple's format) it should hit on every block and discover which the bad ones are (and then mark it as such, and move on).

A format (like a QuickFormat on Windows) doesn't actually touch every byte on disk. It just clears out the indexes that are used to present directories; sort of like having a notepad with a list of scribbled page numbers on the first page; rubbing out numbers on the first page doesn't make the rest of the data disappear, but you also don't find that some of your pages are torn or missing, either).

You might have been able to fix this in Apple's disk utility by formatting with another filesystem (e.g. ext2/Unix) and doing a zero-byte-erase. Then, you do the format with HFS+ (or FAT) and it should have figured out which the bad blocks are by then.

Incidentally, this is why security services never recycle disks, even after they've been formatted/wiped. There's a slim possibility that there may have been data that's written to a 'bad block' and has skipped any wiping attempts, even though some of the information might be recoverable. They all get shredded and destroyed physically ...

The alternative is to place a strategic file over the bad block location, and then not move the block. However, some defrag utilities work by copying files from one place to another, so a defrag will cause this process to fail. But by the sounds of things, the iPod doesn't have track of where the bad blocks are (though I'm surprised that when mounted on the Mac, it doesn't figure it out).

Sometimes, bad block lists become full, and then you start to see these problems. Because there's no more space to store a list of bad blocks, bad blocks will start appearing. That's usually a good time to think about buying a new one anyway ...

BTW a lot of hard drives have logic built in to remap bad blocks, even if the OS doesn't. Probably not on embedded systems like the iPod though.



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