Pending Sector Errors: Re-use or ditch drive?

andrewpdx

April 20, 2010 4:51:11 PM

I use Crystal Disk Info to monitor my hard drives' S.M.A.R.T. status. I've encountered a number of hard drives with "Pending Sector" errors that seemed also to crash the hard drive. In one case, after finding twelve pending sector errors, I ran chkdsk in Windows and although it "recovered" five or six files, it also corrupted them and made them useless (I had backups). In another case, I had a laptop drive that would blue screen however you tried to boot it (even in safe mode); I cloned this drive to another that that one booted right up. The original drive had one pending sector error.

However, after running DBAN on both failed drives to blank them out, all of the pending sector errors disappeared. I might have expected that they would have been replaced by spare sectors, but according to CDI, neither drive has any reallocated sectors or any other S.M.A.R.T. errors anymore. They look like clean drives now.

So how should I view these drives for future use? One was a few years old but the other is only about 6 months old - still under warranty but I can't RMA it I imagine with no errors anymore (it also passes the Western Digital diagnostic with no errors).

Pending Sectors are sectors on the drive that cannot be read, right? What causes them? If blanking these sectors does not cause them to be deactivated by the drive firmware and replaced (as seems to have happened with these two drives), should I assume those sectors are really OK? I had assumed that such drives were basically dying and I should probably recycle them - but could such errors just be glitches that could appear from time to time and not indicate pending hardware failure of the drives, making them no more likely than any other drive to fail in the future?

Thanks for your insight!

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sub mesa

April 21, 2010 1:02:10 AM

When you write to a bad sector ("Current Pending Sector" in SMART output) the HDD will immediately swap it for a reserve one. So one "pending sector" will go away, and the number of "reallocated sector count" should be increased by 1. So it is now a deactivated, non-active, non-visible bad sector that will never be used anymore and cannot cause any more trouble.

The real trouble would be if the HDD continues to produce new bad sectors, even after a full format which you already did. If that is so, i would ditch the drive as it is no longer reliable. If you do not see any more new pending sectors appear; then the drive could last for a long time potentially.

I suggest you download HDTune and check the Health tab; it should display at least these two important stats:
- Reallocated sector count (bad sectors that are swapped and no longer dangerous)
- Current Pending Sector (bad sectors that are not swapped and VERY dangerous!)

The last property should always have a raw value of ZERO. If it is not zero, a format/zero-write/DBAN will make it go zero, as it would swap any bad sector encountered during the write sequence.

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andrewpdx

April 21, 2010 2:58:26 PM

sub mesa said:

When you write to a bad sector ("Current Pending Sector" in SMART output) the HDD will immediately swap it for a reserve one. So one "pending sector" will go away, and the number of "reallocated sector count" should be increased by 1. So it is now a deactivated, non-active, non-visible bad sector that will never be used anymore and cannot cause any more trouble.

The real trouble would be if the HDD continues to produce new bad sectors, even after a full format which you already did. If that is so, i would ditch the drive as it is no longer reliable. If you do not see any more new pending sectors appear; then the drive could last for a long time potentially.

I suggest you download HDTune and check the Health tab; it should display at least these two important stats:
- Reallocated sector count (bad sectors that are swapped and no longer dangerous)
- Current Pending Sector (bad sectors that are not swapped and VERY dangerous!)

The last property should always have a raw value of ZERO. If it is not zero, a format/zero-write/DBAN will make it go zero, as it would swap any bad sector encountered during the write sequence.

Right, but as I noted above, in both cases, the number of reallocated sectors did not increase after I blanked out each drive. The number of pending sectors simply went to zero, and the TOTAL number of reallocated sectors on each drive (according to Crystal Disk Info) is still zero. That means, I assume, that those were not bad sectors in the first place, but for some reason, they became unreadable.

So again, I ask: should I really be worried about the hardware health of the drives in the above case or chalk it up to a "fluke" that can happen to any drive in Windows once in a blue moon, that unfortunately, occasionally, I'm going to get corrupted sectors on good drives and just need to be vigilant and have good, regular backups? In the past, I had assumed such drives were suspect and should be jettisoned.

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