This would be legacy behaviour from the days of buggy ATA33/UDMA implementations, where falling back to PIO mode would allow a device with a buggy UDMA implementation (Unfortunately rather common at the time) to function.
--Adam ----- Original Message ----- From: "Bruce Campbell" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]> Sent: Sunday, January 05, 2003 10:01 PM Subject: Re: ata "fallback to PIO mode" on dual processor AMD systems > Quoting Bruce Campbell <[EMAIL PROTECTED]>: > > > Quoting Matthew Emmerton <[EMAIL PROTECTED]>: > > > > > [ cc'ing Soren since he's the ATA guru ] > > > > > > > Dec 30 23:27:00 ecserv13 /kernel: ad0: trying fallback to PIO mode > > > > Dec 30 23:27:00 ecserv13 /kernel: ata0: resetting devices .. done > > > > > > > > The test continues to run with the ata controller in PIO mode, with > > > > slower performance, and higher load average. > > > > > > > > Once the master drops to PIO, attempts to access the slave then cause > > > > it to drop to PIO. > > > > > > Are you using 80-conductor cables on all your drives? These are required > > to > > > get consistent high throughput, and running without them may cause the > > > problems you're seeing. > > > > Thanks for the information about the design of IDE etc, and the suggestion > > about the cables. I was about to shuffle things to get the disks > > onto separate channels, but I now see that would be a mistake as my > > CD drive would share a cable with a disk. > > ps. As an aside, I have since determined that putting a PIO device and > a UDMA device on the same channel does not affect the performance > of the UDMA device, unless the PIO device is in use. So, sharing > a low use CD rom drive with a disk wouldn't be so bad. > > I am puzzled about the fallback to PIO concept. If a disk has > gives some sort of timeout error or whatever, why would trying > PIO correct the problem ? That seems equivalent to asking the > disk to do the same thing, just more slowly. > > In my case, some sort of timeout error occurs on ad0, so > it falls back to PIO, and works. A later access to ad1 > also yields a timeout error, and then it drops to PIO, > and works too. I'm fairly confident both disks did not > experience media errors at the same time, which suggests > a problem with the onboard IDE controller, or a driver bug. > > Tests continue... > > > > > > > > ---------------------------------------- > This mail sent through www.mywaterloo.ca > > To Unsubscribe: send mail to [EMAIL PROTECTED] > with "unsubscribe freebsd-questions" in the body of the message > To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message