Re: Blockbusting news, this is important (Re: Why are bad disk sectors numbered strangely, and what happens to them?)

[John Bradford]

> Well, consider the two extremes we've seen in this thread now.  Mr. Bradford
> felt that the entire drive should be discarded on account of having one bad
> block.

Please don't spread blatently mis-leading information.

My position on this is that if a drive is _persistantly_ unable to
_write_ to any LBA address, it should be binned.  Read errors are a
separate concern.  If they occur, the drive should simply return an
error.  The OS needs to do _NOTHING_.  No special re-writing to force
a re-allocation should be done - we assume the drive is going to do
that, and if it doesn't:

1. DRIVE -> BIN

2. Restore backup.

> Mr. Machek feels that we should preserve the possibility of reusing
> the bad block because in the future it might appear not to be bad.  I take
> the middle road.  The drive should not be discarded until errors become more
> frequent or numerous, but known bad blocks should be acted on so that those
> physical blocks should not have a chance of being used again.

You may consider that a responsible attitude towards people who are
paying for consultancy, and value their data at more than the physical
cost of the disk, but I do not.

> Suppose the block became readable when the temperature drops (this one
> didn't but I believe some can).  What happens when the block becomes
> readable, and then a program writes new data to that block, and the block
> temporarily appears good?  At that time it will get written and will not get
> reallocated, right?  And a few milliseconds later, what?  I do not want that
> block reused.  I want it reallocated.

1. Monitor drive.

2. Out of spec temperature?  If yes, remount R/O and page an operator.

3. Go to 1

> And when a drive doesn't guarantee reallocation, I want the driver to remove
> the sector from the file system.

Such drives are no better in this regard than ST-506 drives in my
opinion.  I have almost always started discussions with a phrase such
as, "assuming we are talking about modern drives that do their own
defect management".

John.
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