BTW have you seen this before: http://www.iozone.org/ P. Bryan J. Smith wrote: >Peter Farrow <peter at farrows.org> wrote: > > >>No, >>hdparm -t gives you the uncached speed, -T gives you the >>cached speed: >> >> > >You're right, I just looked at your numbers incorrectly. I >was wondering how you got 62MB out of the Ultra33 interface, >but didn't see it was for 3 seconds (doh!). > > > >>The disks are set the logical block assignments already, >>and anaconda, detects the number of cylinders differently >> >> >in > > >>the install, which makes mirroring non symmetrical, trust >> >> >me > > >>when on channel 1 and 2, I've checked this in great detail, >> >> > >First off, if you use Anaconda with the master/slave on the >primary, and the BIOS is LBA, then the partition table _will_ >be created with LBA. After that point, if you move the disk >to the secondary channel, it _will_ continue to be LBA -- as >Linux will read the geometry from the _disk_, not the BIOS. > >Secondly, you can _force_ different geometry by pulling up >fdisk and entering "x". Then manually set the "h" (heads) to >255, and the reduced "c" (cylinders) appropriately to match. >Hit "r" to return to the main menu and "o" to install a new >partition table. > >_Everyone_ needs to know how to do this -- especially when XP >forces 255/63 in conflict with the BIOS on regular >occassions. Ironically, this is no longer LBA48 compliant, >and heads can exceed 255 now (don't get me started). > > > >>furthermore, simultaneous requests to both drives isn't >>affecting performance as much as you imagine, here are the >>results of a simultaneous hdparm test: >> Timing buffered disk reads: Timing buffered disk reads: >> 46 MB in 3.08 seconds = 14.93 MB/sec >> 46 MB in 3.08 seconds = 14.92 MB/sec >> >> > >First off, that's a 25% drop right there! > >As I said, you're not only seeing a 50% drop because of the >sharing, but additional overhead that could be up to 80% >less. I'm sure if you make a sustained set of transfers, it >would really kill it. The resetting of the ATA bus >continually is part of the problem -- although you're using >the same type of disk/mode, so at least it's not as bad as it >could be. > >(E.g., putting a PIO CD-ROM on the same channel as a DMA hard >drive typically results in far more than an 80% loss with all >the reset overhead). > >Regardless, 15MBps is about 3-4x _slower_ than modern disks. > > > >>Also the old machine had them on the same channel two for >>the same reason..... >>This isn't the issue, its something else....... >> >> > >Oh, why didn't you mention the old config was the same? > >-- Bryan > >P.S. In a world with cheap, off-chipset Ultra33 cards >(sub-$10 at many resellers) for additional channels (such as >optical drives), why ever put two hard drives on the same >channel? > > > >