Errors on Hard Disk

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I was reading up on something and it said if you develop errors on your hard disk, the first thing you should do, is a thorough scandisk, which I thought was fair enough but it also said that if you do a defrag before the scandisk, then this could make matters worse… Why?

EDIT: the only thing i can think of is that defrag moves the files around? but files are software and those errors are physical errors so i still cant think of it?

 

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A single error on a HD usualy means that there are more either hiding or waiting to happen. Doing lots of writing (which is what a defrag will do) could easily tickle those weak or dud sectors.

IMHO the *correct* thing to do with a HD with a hard error on it is to make sure your backups are good, and replace the drive. IMHO a scandisk is a waste of time!

Harry.

 

What about utilities such as Norton's disk doctor or System mechanic ?

 

or spinrite (http://www.grc.com/sr/spinrite.htm). imho steve gibson is an alarmist fool, but at least he created an awesome product with spinrite. saved my ass a couple of times.

 

great link, thanks D

 

Do not modern hard drives automatically mark physically bad sectors as unusable? I don't know why I think this, must have heard it somewhere.

 

Yes they usualy do. They often also have a few spares in a hidden area that can be - in effect - swapped for a bad sector.

Because of this when the spare set runs out and you see an actual bad sector it means that the drive is on its way out - hence my comment about replacing it *now* rather than trying things like scandisk on it.

Harry.

 

That makes perfect sense. Any idea how many spare sectors are set aside generally? I can't see it being more than a few meg.

 

I don't know details - but I would agree that it won't be many.

More here .

Harry.

 

TheCheekMaster,

To answer your question, let's review what each application does.

scandisk basically looks at all sectors for corruption. No corruption, no problem, move on. However, if corruption is found, then it attempts to fix the corruption. If corruption is unfixable, then the sector gets marked as unusuable.

defrag basically reorganizes the sectors involved in a single file in an undefragmented orderly way.

Now, let's look at scenario 1 where scandisk is done before defrag. So scandisk would make sure each sector on the entire hard drive is ok first. Kinda like checking if streets have pot holes. If there's a pot hole, the pot hole is fixed. After the pot hole is fixed, then defrag puts the sectors involved in the files into an orderly fashion.

Now, let's look at scenario 2 where defrag is done before scandisk. Going back to my pot hole analogy, that's like moving all sectors of a file into an orderly fashion, even the sectors with pot holes. Since defrag is primarily a reorganizing program and not an error detection/correction program, defrag may possibly "hang" while trying to move a corrupted sector. Now, let's say the file has been somehow defraged. Now run scandisk. Well, scandisk will notice the pot hole in one of the sectors of the file. It will try to recover the sector. But what if the sector is unrepairable? It gets marked as "ususable." So now you've got a defragged file with one of the sectors marked as unusable. Now you might be able to see how things are "worse" because now you've got an unusable file because not all sectors associated with the file are usable.

Just trying to help.

 

Good answer there mate.

 

Cheers Harry and R.H.Lee