WD2010 / No ECC

[Clarence Dold]

in article <1624 at mtunb.ATT.COM>, jcm at mtunb.ATT.COM (was-John McMillan) says:

> Several people have made assertions about installing the WD2010:
> 	1) It has (a) reduced errors, or (b) recovered 'lost' disks;
> 	2) It must be the Error Correcting Code [ECC] that does this.

> I don't dispute (1) and am happy this chip helps.  We all need
> 	a break once in awhile ];-)

> However, these references to ECC are fanciful or an incorrect
> 	use of the term.
> 	there is NO kernel support of ECC.  

> 	It would be nice were the ECC supported -- but I've never
> 	even identified a way to figure out WHICH chip is plugged in:
> 		a) W.D. technical support said THEY had no idea of
> 			how to figure this out.

Indeed, there is no ECC support in the kernel, and it would require a 
reformat of the disk if it did.
The chip merely informs the system of an ECC error.  Some systems leave
a 'Track Buffer' intact, for the 2010 to make the change, others must
locate the data, wherever it has been transferred, and make the change there.

I don't recall the detail, but detecting the presence of a 2010 vs a 1010
on a machine that could have either was done by setting a cylinder register
to 1200, then reading it back.  A WD1010 would modulo 1024 the register,
a WD2010 would return 1200.

> Since IT AIN'T THE ECC, wherein lies the magic of the WD2010?
> 	Without getting into the theory of how a Phase Lock Loop [PLL]
> 	works -- which would be ridiculous for ME to try 8) -- let's
> 	just assert a smarter PLL circuit makes fewer errors in

The PLL isn't on the chip, it's external.
The chip itself might be better...

Try setting the Step Rate in an iv.desc file to 14 instead of 0, 
then iv -u the disk.  No loss of data, just a 20% increase in seek performance
on 28mSec disks.

Ignore any significance in my signature.
I don know nuddin about the Unix PC.
The iv part, in particular, is untried, untested, and subject to failure.
(but somebody that is well backed up should tell us if it works.)

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