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SubjectRe: Fujitsu can't work properly in UDMA2 mode
On Mon, Dec 21, 1998 at 09:49:59AM -0800, Alan Olsen wrote:
> > > My problem with my HD was something similar. When I bought my new computer
> > > I change the speed of my Pentium II 350 to 396(+-) and the UDMA did not
> > > work properly, and the Hard Disk gave CRC errors. I cannot understand why
> > > the hard disk have problems when I change the speed of the processor. Is
> > > the procesor the checker of CRC of the disk? When I disable the DMA with
> > > hdparm the error disappear.
>
> I am seeing similar errors on my home system. The interesting thing is that
> these errors started occuring only with the development line of kernels.

The problem here is a hardware one -- overclocking a multiplier-locked
processor such as a Pentium II (modern ones) requires upping the front side
bus speed. In this case, the original author (attribution lost) raised his
FSB to the 112MHz setting (although the BIOS seems to actually use a 113.xMHz
setting for this purpose).

The problem is, this raises the PCI bus speed from 33MHz (100MHz / 3) to
37.7MHz (113.xMHz / 3). Many hard drives simply will not be able to transfer
data at this rate using the most aggressive data transfer methods like UDMA,
DMA/33, etc.

The problem is probably occurring under the newer kernels because they
transfer data quicker than the old ones -- hence, greater chance of data
corruption.

People having these sorts of problems may wish to change their settings to use
a slower transfer mode (one of the PIO modes) to reduce the chances of error --
although the impact this has on system performance is noticeable, and probably
a Bad Thing (TM) when the whole point of overclocking is to raise system
performance.

Charles Cazabon


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