Re: EXT2 and BadBlock updating.....

[Rogier Wolff]

Alan Cox wrote:
> > Reading this thread, I see that many have a misconception. Bad blocks
> > will not be found when someone tries to write to a bad sector! As
> 
> Actually on IDE and modern SCSI disks they will be. The drive does it for
> you without you knowing. It also schedules its own I/O, it lies about
> geometry and it does transparent block remapping.

I've been wondering about this for years. I've seen drives "grow"
defects. For example, over 10 years ago, I accidentally bumped my knee
against the underside of the table where the computer was sitting.
Bang! 5 bad sectors!

Similarly, I've seen IDE disks get bad spots. Wether that's due to
marginal blocks getting OKed at the factory, or physical abuse, I
don't know.

On SCSI disks, I've also seen the term "grown defect list" which on
good disks tends to be empty. However, the provisions are there.

Anyway, if a disk finds a block to be unreadable for some reason, it
cannot do anything else but report error. Possibly if you issue a
write request for that block, it could reallocate the block, however,
I've tried "fixing" disks with badblocks by doing a 

	dd if=/dev/zero of=/dev/<disk>

but the bad blocks remained in place. 

So how DO I trigger a reallocation of a grown bad block?

				Roger.

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