# The HDD knows there's a bad block, but wont reallocate.

## dE_logics

In my short experience as a Linux administrator and having serviced ~10 PCs, I've encountered a spiked error rate of 3 HDD failures, the latest being a seagate HDD.

This one shows a self-assessment test result: PASSED but the short and long diagnostic checks end up in around 1 second with Completed: read failure @90%. I ran these tests cause the installed Ubuntu OS suddenly refused to boot and mounting the partition was showing very awkward behavior.

There's just one bad block in the whole hardrive, but it has not been reallocated; i.e reallocate sector count is 0 but current pending sector count is 1. I've noticed this in another Seagate HDD but it was not giving a problem, but the guy complained that he had to reinstall windows more often than others (i.e every 2 days rather than a week)...so I did have a doubt about the HDD since windows always showed missing files to be the problem.

So final question is why is this read failure occurring...is it cause of the single bad block which's pending reallocation? or some other reason?

This problem has to be Seagate specific since I've seen HDDs with like...800000+ bad blocks but 0 unallocated...it was a hitachi HDD. Another one was a WD with 125 bad blocks but all reallocated.

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## aderesch

 *dE_logics wrote:*   

> This one shows a self-assessment test result: PASSED but the short and long diagnostic checks end up in around 1 second with Completed: read failure @90%. I ran these tests cause the installed Ubuntu OS suddenly refused to boot and mounting the partition was showing very awkward behavior.
> 
> There's just one bad block in the whole hardrive, but it has not been reallocated; i.e reallocate sector count is 0 but current pending sector count is 1.

 

Reallocation normally only happens during writes to the sector in question. Have a look at this:

http://smartmontools.sourceforge.net/badblockhowto.html

The easy (but lengthy) way would be to do a non-destructive badblocks run on the whole drive -- it should get rid of this pending sector and possibly other problematic ones that haven't been marked yet, but you can't use the drive during that time.

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## dE_logics

Thanks, I'll try it out on his HDD.

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## aderesch

 *dE_logics wrote:*   

> Thanks, I'll try it out on his HDD.

 

Just in case this wasn't obvious I should probably point out, that there is a non-zero chance of the sector already being unreadable (instead of only requiring a large number of retries). In this case you might loose data and have no indication of which file or filesystem metadata was corrupted. Finding that out first (see the linked howto) would enable you to restore from backup or reinstall the corresponding package. Following up with an fsck is a good idea either way.

That said, the only data loss I have encountered so far was on a drive that almost certainly had been running with a "failing now" state for quite a while.

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