"Bad Sector" False Positives: Bad blocks caused by write errors?

[soldier9599]

Are bad sectors always irreversible hardware problems? How do programs test for bad sectors, and could it be possible for soft data errors to come up as damaged blocks even if they are physically just fine?

I recently had a drive come into my possession that had completely failed within the laptop it was used. The Windows 7 system failed at every boot, CHKDSK (run from installation media) would spend days on end trying to make repairs, and reformatting and reinstalling Windows was unsuccessful. So the first thing I did with this disk was plug it into my desktop and run a surface test in Paragon Hard Disk Manager. It found tons of bad sectors and I was convinced the drive was trashed. The weird thing was there were two partitions, and only one partition had errors, so I suspected maybe it wasn't purely a hardware problem.

To test this hypothesis, I wiped the entire drive to zeros and told it to verify every bit. There were no errors! I then ran another surface test on extreme mode and found no bad blocks! I then formatted the drive to NTFS and scanned the file system in Paragon with slightly enigmatic results. It came back saying there are no bad blocks and listed no problems in the log, but for some reason it said there were "minor problems." As expected, viewing it in any file manager (showing hidden) shows nothing, and dir in cmd comes up as "file not found," but strangely the file system test said that there were 11 directories and 27 files. I ran CHKDSK and Windows told me that it found no errors. I could run another surface test, but I'm worried that if I keep testing and testing I might encourage this drive to move closer to the end of its life.

Were the bad blocks I found simply caused by write errors or temporary data damage? Is it possible that most of the ills of this drive were fixed by the wipe? Or is it more likely that this is only temporarily masking the real problem, and I will very soon see problems again? I know it's impossible for you to know for sure, but I'm wondering what your experiences would lead you to predict.

 

[rdc85]

AFAIK bad block sometimes not a full damaged sector/block, sometimes it's just a weak sector/block but marked bad to avoid system/os to write data there to avoid damage to the data..

as an example some bad block is not growing even after weeks, month... this most likely happened..
but with block that damaged because scratched by pinhead it will continue to grow..

for your case have u check the drive size? usually the total size is reduce from the before u wipe it clean...
(that technique is usual used by "bad" second/used hdd seller to mask the bad drive, and sold to uninformed buyer)
the Bad block will come back later..(growing)

anyways I recommended u to not use that drive again...

well, that's what i think/opinion

 

[soldier9599]

Thanks for your help. The total size is roughly the same, but I didn't make a record of the exact number of blocks on the drive. I guess I'll just assume the drive is bad.

 

[Paperdoc]

The key to your mystery is the beginning of your third paragraph. There you say you "wiped the HDD to zeros" and it magically had no errors!

All modern HDD's have several self-checking and correction processes built in and NOT commonly apparent to the OS (Windows). When you Zero-fill a HDD, what that does it write all zeros to EVERY Sector of the HDD. As each track full of Sectors is written, it then re-reads all those Sectors to check for errors. If it finds any Sector returns bad data, OR even if the signals read from it are weak, the HDD will retire those "bad sectors" from use and replace them from a stock of good spares. You see, at the time of the real "Low-Level Format" done at the factory, the HDD has more good sectors that it needs for its stated capacity, and the spare ones are noted in a special file area of the HDD. Replacement good Sectors are drawn from this. So, by the time a Zero Fill is complete, ALL the suspicious Sectors ought to have been replaced with spare good ones. If you then run a diagnostic, or Windows' CHKDSK on that unit, it should find NO Bad Sectors. Windows does not know anything about this seemingly magic fix.

This same process of checking the quality of the data signals on a Read operation should happen during normal use. If the HDD thinks the Sector accessed is "bad", it will run several techniques to try to recover reliable good data from it, copy that to the new replacement Sector, and then retire the "bad" one. It won't even report that to Windows. BUT it it cannot recover good data, THEN it will tell Windows that a Read Error has occurred.

Of course, there is a limit to how much of this self-repair can be done. When the stock of spare known-good Sectors gets down to a trigger level, the system writes a warning message to the HDD's SMART system, and you get a message to tell you that. At this point the HDD is still working OK and it is VERY likely that your data and files all are OK. BUT this warning says two things: (a) the spare good stock is getting low, so self-repairs cannot keep on too much longer; and, (b) there have been a lot of such errors, which MAY imply that things will get worse at a faster rate, so NOW is the time to buy a new HDD and clone all your data to it BEFORE a serious error causes data loss.

What you did "fixed" all the "Bad Sector" problems that Windows can find. Now you should use a disk diagnostic test utility suite to check your old HDD thoroughly. First, check the SMART data report and see whether there are any warnings of imminent failure. Next, run the Short Test and, if possible, the Long Test, to check the HDD completely. Most utilities of this type do NOT destroy your data when these tests are run. However, many also include some additional data-destructive test and repair utilities that should warn you of data loss BEFORE you allow them to execute, so watch for warnings as you use the test suite.

 

[rdc85]

Thanks for the info paperdoc..

it's quite detailed.... 😀