Caveat User: CHKDSK is NOT a solution

This posting should be made sticky.

Periodically, we see postings that indicate that there are bad sectors on a drive.

And a number of users think that they are OK if scandisk or chkdsk "repairs" the problem.

Well, that ain't necessarily so.

Each drive has a fixed number of spare sectors that can be used to replace bad sectors.

When chkdsk repairs a sector, it may be just pulling a sector out of the pool of spare sectors. When 1 sector is bad, there are usually others, perhaps many, that are bad.

So, even if chkdsk repairs your problem, you still need to run the diagnostics supplied by the drive manufacturer, and, if any, those of the SCSI or other drive controller card.


Here's the advice:

 

I had always thought, perhaps wrongly, that spare sectors are created as part of a HDD's manufacturing process to ensure an acceptable yield of good drives . The fact that there may be spare sectors left over which can be brought into use by CHKDSK/R whilst convenient for users is to my mind only applying a Band-Aid to a failing drive.

After running CHKDSK it is vital that the results are checked. The results, which only appear fleetingly, for an in use drive can be found for XP systems in the Event Viewer log under Appliations/Logon. I would take a report of bad sectors as an indication to fit a new drive ASAP.
After all how many failed sectors is a user expected to accept before the supplier will replace the drive ?

Xpilot.

 

Spare sectors are present because the architectural design, i.e., the standard, for the particular drive specifies such sectors be recorded.

I am referring to the situation in which users get a false sense of security when a disk has bad sectors and chkdsk appears to repair the errors.

It is still necessary to run the proper drive manufacturer and controller manufacturer diagnostics to find the true state of the sectors on a disk. Sectors usually go bad in bunches. It is necesary to get as early a warning as possible.

 

Normally there is a hardcoded (ROM) on the drive electronics which has a record of all the bad sectors that are known at manufacture time - subsequently the firmware and software drivers will not place anything in these areas - as far as the end yser is concerned they just don't exist.

However if a low level formatting utility is used - this sector information becomes mismatched - and all hell can break loose.

Colin

 

Thanks for your clarification Bodgy. I had understood from Howard's post that CHKDSK/R actually repaired bad sectors by bringing "Spares" into use. As I have never had a bad sector reported on any of my hard drives I had taken what he said at face value.

But, or should I say when, I get a bad sector reported I will in any event replace the drive ASAP.

 

The bad sdectors that are marked at the factory have nothing to do with the "spare sectors" I am referencing. Of course, the fewer the factory formatted bad sectors, the more spare sectors there would be.

THe spec for each drive, be it a standard or proprietary format, will specify that a drive must have a certain number of spare sectors. No reputable manufacturer will ship a drive that violates that spec.

Spare sectors are extras that will NEVER be used unless it is determined that one the good sectors that left the factory gets bad,

chkdsk does not necessarily replace a sector with a spare.
It might merely update a CRC, or some other critter, to make the sector consistent. Spare sectors are used when a sector is PHYSICALLY bad.

The point I was trying make, albeit after pulliing a few all-nighters doing my taxes, was that even if chkdsk appears to fix things, one should still run the diagnostics to see what else is bad.

It's normal for a few sectors, here and there, to go bad, that's why spare sectors are provided.

But sometimes youse is left up the creek without a paddle.

A bit over a year ago, whilst I was sitting at the computer, I actually heard the heads crash on my NEWEST drive. Fortunately, I had just done a backup about 2 hours earlier, and I back up my active programming projects to a ZIP drive, so little, if anything was lost.

About 7 years ago, the drive that originally came with the PC suddenly had so many bad sectors, I could not use the drive without reformatting and leaving off about 1/3rd of the drive. Again, I was fortunate, as I had done a backup the day before.

In both cases, I might have ben able to anticipate the problem if I had periodically run the diagnostics.

Oh well, do as I say, not as I do!

 

While this thread is discussing bad sector problems I think it should be mentioned that a chkdsk /r does the steps of a chkdsk /f as well and fixing the disk may be nothing more that fixing up a bad files structure that was caused by something other than a bad sector.

On low-level formatting, IMO, if your drive requires a low-level format it should be junked. Low-level formats on IDE drives are intended for the life of the drive so something nasty must have happened to it.

I consider a bad sector report to be a warning that the drive is going bad and to take the appropriate steps in advance of total disaster.

Howard is right, if bad sectors are revealed, the problem may well permanently resolved.

 

A workable strategy would be to run the drive dagnostics periodically (another do as I say, not do as I do).

All drives have come way down in cost.
My drives are all SCSI,so costlier to replace.

 

About a year or so ago I had a situation where a faulty IDE cable caused corruption of the low level format. The manufacturer's diagnostic would not recognise the disk. Windows 2000 would not recognise the disk and consequently it could not be formatted. However SpinRite 6 did fix the problem. A couple of data files had to be restored from backup which was no big deal. Other than that there was no other problem, no need to format or anything. That disk is still in daily use today.

 

I guess nothing should ever be stated in absolute terms.

My thought was along the lines of considering a low-level format as a way to fix the disk when bad sectors start popping up. This was an accepted fix for old RLL (pre-IDE) disks. It seemed the format information used to "fade away" after a period of time.

 

Few folkes have accces to the equipment needed to do a low level format.

Drives are so much less expensive these days,doing a low level format wouldnot seem to be worthwhile.

 

I guess that was due to the magnetic strength of the recording gradually becoming weaker.
SpinRite 6 can fix this situation. It can also recover 'bad sectors'. As well as fixing the corrupted low level format data I mentioned above. Not exactly sure how it does it but I guess you could say that it analyses the structure of the magnetic signal then boosts the signal whilst eliminating spurious noise so that the original data can often be recovered. It is obviously not a simple process since it can take many hours to work its magic. So it's not a low level formatting utility but more a recovery tool for when the magnetic nature of the recording is somehow corrupted.
It's not cheap (about the cost of a hard disk) but should you really need to do your best to try to recover a corrupted disk it's worth every penny.
Unfortunately there's not a demo version but there is a 30 day refund period if it doesn't help you. (No - I don't get a commission!)
For those interested further see: www.grc.com