[Techtalk] bad blocks

[Rudy Zijlstra]

R. Daneel Olivaw wrote:

>Hi,
>
>Hard drives develop bad blocks because of the physical way they are
>built. Hard drives are disks with a layer of magnetic aware matter.
>Writing a disk is exposing a piece of magnetic sensitive matter to an
>electro mgnetic field. The matter then changes magnetic orientation.
>Reading a disk is to apply a lower magnetic field and to "sense" the
>magnetic orientation.
>It occurrs, because of the small size, that some parts loose their
>ability to store magnetic information. Therefore, some 'blocks' are bad,
>after a number of read/write cycles.
>
>  
>
There is yet another reason. Because we are talking moving parts, it can 
happen that the tracks start wandering. This can be seen by getting bad 
blocks on a track (cylinder) order. This happens because positioning is 
- though very accurate - still something with an error margin. And at 
times that margin works out wrong. Some drives are more sensitive to 
this than others. When this happens, the bad blocks can sometimes be 
recovered by writing to the complete tracks, and that way "resetting" 
the track location signals on the platter. On a SCSI disk with this 
problem, giving the low level SCSI format command will also solve this.

>If you have faulty blocks, you may use all of the disk, perform an in
>depth formatting, marking all blocks, but ... I would say that with
>time, if your drive has more and more bad blocks, you should change it.
>Hard drives are really cheap, and the time loss (worse : data loss)
>really is worth the change. Once a disk starts being damaged, you will
>loose sleep not being able to trust that hardware.
>
>Well, as far as I am concerned, I would wipe that drive out and use a
>newer, probably faster and smarter one.
>
>  
>
Agreed.

Cheers,

Rudy