How can I determine what a bad sector affects?

Started Mar 8, 2013 | Discussions thread
Sean Nelson
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Re: How can I determine what a bad sector affects?
In reply to malch, Mar 27, 2013

malch wrote:

If the drive (firmware) knows about this bad sector, it's already been mapped out and isn't being used for data.

scokill wrote:

Windows should mark the bad sector and not use it for data storage.

If data in a sector has "gone bad" since it was written, then the drive will report an error whenever you try to read the data.   The drive marks the sector as "pending", which means it needs to be remapped but still contains data that hasn't been read.   The sector will remain in this "pending" status until new data is written into it.

This is done because there's still the chance that the data in the sector can be successfully read, and until the sector is overwritten the drive's responsibility is to retain the data.  So it won't remap sectors until it's able to either (a) successfully read the data from the sector (at which time it will copy it to a spare), or (b) overwrite the sector with the new data supplied by the user/software/OS (at which time it will also write the data to a spare).

You can tell if a drive has bad sectors like this by looking at the SMART data and checking the "pending sector" count.

The way to identify the bad file is to read all of the files on the disk and see which one gives an error message.   You'd need to do this using a file-based read method, as opposed to an image-read method.  A backup program that does file-by-file backups should tell you, as long as you can force it to back up every file on the disk.

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