Dban and bad sectors

General Questions
#1

I saw a couple threads on erasing hard drives recently and got me to wondering about something I heard a couple of years ago. When I bought my new computer, I decided to wipe any personal info from my old computer before selling/disposing of it. I decided to use DBAN, and it seemed to work as stated, however I was later told that using such utilities was “bad” for the computer as it erased the partitions that the manufacturer put in to block access to bad sectors (which I was told all HDs have.) Since they are no longer sectioned off, the computer does not know not to write to these sectors.
I read the faq at sourceforge and it seemed to say that dban does not write over “bad sectors”. It seems to say that it doesn’t even have access to those sectors.

  • Is overwriting an HD with such a utility “bad” for the HD?
  • Does in erase those “neccessary” partitions? (And can those sectors be sectioned off again?)
  • If not, are there similiar programs that do, and should they be avoided?

What’s the dope?

#2

What you list as fact is a jumble of statements. I’ll address the points that I get out of it.

Hard drives can mark sectors as bad, not to be used for storage. I don’t really find bad sectors on most drives anymore. You can run an advanced scan of the hard drive to check for bad physical sectors. Any undependable sectors will once again be labeled as bad.

I haven’t used the program you mention, but it likely rewrites every sector of a hard drive, as opposed to just the File Tables. It may even write multiple times over the sectors. It’s like doing a low level format. It won’t hurt a drive that isn’t on the border of failure. Most hard drive utillities when doing full formats will check to make sure the sectors in a partition are good, and mark them bad if they are bad. You can always run the advanced scan.

#3

I don’t know anything about DBAN, but in general you don’t have access to the “hidden” areas of the drive that are used for error correction. These are handled internally by the drive. They aren’t “normal” partitions and sectors and such that appear external to the drive. When you access a “bad” sector, the drive automatically reads/writes the data from the “hidden” area. It doesn’t tell the computer that it didn’t really read in the sector that the computer asked for, so there’s no way for the computer to really be aware that it even happened.

In other words, your computer asks for head 3, track 4, sector 2, and the drive gives it the data. If the drive did something funky and that’s not really where the data is, the computer doesn’t realize it. When you “format” the drive, the computer doesn’t bother to go through every track and sector and wipe out any data that is there. Instead, all it does is mark that track and sector as “available” to the operating system. All the data is still there, it’s just that the index to it is gone. Drive wiping programs like DBAN actually go through and write new data to each track and sector. Sometimes they write all zeros to clear out the data, which is good enough to prevent the average snoop from finding anything you left on the drive. If the program is particularly paranoid, it will write different patterns over and over to the tracks, which makes it more difficult (but not impossible) for the FBI guys to figure out what the data originally was if they really take a close look at your drive.

A hard drive manufacturer may have special utilities available that can access the disk at a much lower level, but anything general purpose isn’t going to have access to the stuff you are talking about.

#4

I wasn’t attempting to list anything as “fact.” As I mentioned in the first sentence, I was

I just wanted to clarify the accuracy of what I was told, as it did not seem to jive with what I was reading on the sourceforge page.

The program in question is Darik’s Boot and Nuke (DBAN), and does write over the HD in multiple passes (1 to 35 times I believe). It’s my understanding that simply formatting the HD does not actually erase any data, but rather just changes the pointers (is that the right term?) to show that space as “available”.

I was just wondering if DBAN (or any similiar program) REALLY DID overwrite all sectors, even “bad” ones. And if so, did this introduce problems when reinstalling an OS, since bad sectors were no longer sectioned off.

#5

engineer_comp_geek covered it as I was posting I guess. Thanks for the info. That seems to be what sourceforge was saying. It seems that DBAN should NOT have access to any sectors the manufacturer chose to section of as “bad” or “hidden”.

#6

Bad sector management used to be handled by the OS. When you bought a drive, it would come with a little printout saying where the bad sectors were, and when you formatted (or re-formatted) it you would enter in this list of sectors.

During use, if the drive developed a bad sector you’d either have to scan for it and mark it bad, or the OS would do that automagically (can’t recall when the latter became de rigeur). Formatting would blow away all this bad-sector data, and you would have to enter it again. If you did a low-level format, chances are the bad sectors would be detected and marked bad at that time.

Nowadays, if your HD is failing to the point that the OS is having to step in, it’s got a lifetime measured in days at the most.