On Thu, 21 Oct 2004 23:47:11 +0200, Robert Epprecht <epprecht@xxxxxxxxx> wrote: > Mark Knecht <markknecht@xxxxxxxxx> writes: > > > On Thu, 21 Oct 2004 19:43:16 +0100, anahata <anahata@xxxxxxxxxxxxxx> wrote: > >> On Thu, Oct 21, 2004 at 07:44:11PM +0200, David Baron wrote: > > >> > was told that the slower CD device will slow down the HD. > > >> It used to be true. It was often misrepresented as the CD slowing the HD > >> down to its speed > > > No - this actually is true. An EIDE controller that is compliant with > > the ATAPI specs will recognie that one drive operates with the cable > > going 100MHz, while the controller recognizes that the CDROM only > > works when the cable goes 33MHz or 66MHz. since the two drives are on > > the same cable the EIDE controller sets the cable speed at 33MHz and > > therefore you get less throughput from the hard drive. I wasn't aware > > until about 2 years ago that the controller had to do this. There are > > some good white papers somewhere on the Seagate or Maxtors sites if I > > remember correctly. > > So you say, that it is the *controller* who does it? > It can not be influenced (set) by the kernel, by hdparm or something? No - it's done in hardware. If one drive REQUIRES that the cable run at 33MHz, and the other drive can operate at 33/66100MHz, then the controller sets the cable at 33MHz and leaves it there. The EIDE cable cannot change frequency while operating. I think the good news is that your equipment looks new enough that you will likely not have this problem. It's more an issue when mixing new and old hardware. > > This sounds like it could be easy to figure it out with dmesg, hdparm > or something comparing results with and without connecting the optical > drive? What exactly should i look for? Sure - run: hdparm -tT /dev/hda with and without the optial drive attached. (Optical should be /dev/hdb) Do it again with the second drive using hdparm -tT /dev/hdc > > Robert >
