Offline Uncorrectable Sector Count

[PeteB]

I have had an issue with a couple of bad sectors on a hard disk. Initially the short test and extended test failed. I ran a disk read test which highlighted a couple of bad sectors and ran a surface reinitialisation which completed successfully. The hard disk returned to 99% health.

Prior to returning this hard disk to service, I would like to understand one value in the SMART attributes. This is the offline uncorrectable sector count. This currently has a value of 1. My understanding was that if the surface reinitialisation completed successfully this value should be 0. Could you please advise if I still have a problem to deal with. I have attached a screen shot of the relevant disks smart data:

Snap1-hdsentinel.jpg (69.56 KiB) Viewed 52093 times

[hdsentinel]

The value of 1 of the mentioned "offline uncorrectable sector count" S.M.A.R.T. attribute indicates that the hard disk reallocated one bad sector: as that one sector was physically damaged and should not be used in the future, the hard disk marked it permanently as bad and then re-directs all further reads and writes (targeting that sector) to the spare area.
So that one sector can never cause problems in the future.

Generally, this is the purpose of the mentioned Disk menu -> Surface test -> Reinitialise disk surface test: to force the hard disk to verify the actual situation, check the consistency of the sectors (which previously appear as red on a read test) and

1) if the sectors can be used, they can hold the data without problems (which is confirmed by the test, because of its numerous overwrite passes and verification of the stored data) then the sectors return to normal status. This usually happens if previously "weak sectors" reported in the text description, which may not indicate real hard disk problems, but can indicate problems in the operating environment (eg. overheat, cable/connection issues, etc.) which can lead to data loss.

OR

2) if the sectors are damaged, the hard disk performs the re-allocation which confirms that the original (bad) sector will be no longer used.

This is why generally some such bad sectors can be accepted - if their number is relatively low and the status is stable: there are no new problems detected with time.

I recommend to click on the "?" button next to the text description area of the software, which describes the meaning of this situation (about bad sectors in general).

Also you may check the following sections of the Frequently Asked Questions page:
http://www.hdsentinel.com/faq.php#health
http://www.hdsentinel.com/faq.php#tests

For more information (if weak sectors reported previously):
http://www.hdsentinel.com/hard_disk_cas ... ectors.php

[PeteB]

Hi,

Recently I received a notification from HDSentinel, that the offline uncorrectable sector count decreased from 1 to 0.

I am trying to understand what this means. The SMART data from the hard disk also shows this value as 0.

My understanding was that offline uncorrectable sector count indicated the number of permanently bad sectors that were remapped. If this is the case, how would this number decrease.

Kind Regards,
Pete

[hdsentinel]

Yes, generally this is true: the number of reallocated sectors (replaced by sectors from the spare area) should not decrease.
But some manufacturers may use the counters in a slightly different way: when the amount of problems is relatively low (the counter was 1), and because of the fact that the reallocated sector(s) can never cause further problems, after some time of stable use (with no additional issues detected) the counter may decrease back from one to zero.

Of course this does not mean that the hard disk will re-use the original sector (already confirmed that should not be used and needed reallocation), just because that one sector causes no further issues, it is no longer reported.
This is same as you'd manually clear the error-counter (as described at http://www.hdsentinel.com/faq_repair_ha ... _drive.php ) to acknowledge the problems to get notification only about further issues - just it is done automatically now.

Can you please use Report menu -> Send test report to developer option? Just to check the actual hard disk model and its current status.

Personally I'd perform some testing, as described at http://www.hdsentinel.com/faq.php#tests
At least with the non-destructive (safe) tests:
1) Disk -> Short self test
2) Disk -> Extended self test
3) Disk -> Surface test -> Read test
to verify the status, to confirm that the drive is now stable - there is no further problem with the disk surface - or to reveal any possible issue with the disk surface.

[PeteB]

Just wanted to publicly say a big thank you to Janos for his assistance!

I sent him the disk report and as promised he analysed it and returned a response.

I have some other software which is not inexpensive and provides software raid capability, and the support is scant and the responses almost churlish. It is quite refreshing to see someone stand by their product and provide genuine assistance to users.

Well done and I will be recommending this product to all my friends.

[VGER]

Hi,

also thanks from me for the clarifications - I had a situation like that myself a few days ago:

Drive health went 100 -> 99. SMART data showed one sector "pending".
"Short self test" passed.
"Extended self test" failed.

I then started a surface test ("reinit", the most extensive one, including rewrite.)

During the test, the "pending" went 1 -> 2.

As the test progressed, "pending" went 2 -> 1, later 1 -> 0. After the surface test, health was reported as 100.

The SMART data for "relocated" or "offline sectors" never increased, both are still zero.

Based on what you explained I think I understand now what happened: Either the sectors were just "weak", but not "bad", and no relocate ever occured. Or the drive firmware decided that the single sector (it had been pending and stable for over a year or so) was not worth a warning.

As said, thanks for the explanation.

Regards