On Thu, Feb 14, 2008 at 9:59 AM, Randall R Schulz
On Thursday 14 February 2008 06:18, Greg Freemyer wrote:
...
Per,
I don't know how you measured the load, but it is important to measure very short power surges. In particular, I'm suspicious of that load during raid1 resync. Could your technique catch a 10 msec spike etc?
Surely the capacitors in the power supply and elsewhere would absorb such brief demand spikes, no?
And what is their source? Logic circuits active only transiently or the voice coil? Obviously the spindle motors have uniform demand once the drive is spun up (but much higher while starting up, of course).
I'm guessing disk seek activity. As the seek activity is getting faster and faster, it takes more and more power to start/stop the heads as they skip around the drive. Apparently if you don't have a very solid PSU, the sata drive starts encountering problems. The trouble with that theory is I would have hoped the drive motors, etc. would be 12v and the electronics 5v, so I really don't understand how the issue happens either. Especially since disk seeks are on the order of 1 or 2 millisecs and a relatively small cap should handle that fine, I did just go back and re-read one of the posts and Tejun Heo said the issue is with the 12v supply and the new video cards that are sucking up all the 12v power. Regardless, most of the reports I have seen have been with 4 or more drives, especially in a raid 5. So it seems that the actively of one drive is causing problems for other drives sharing the PSU. On the lkml-ide list, the very first troubleshooting question for this type of issue is to power up the drives from a separate PSU. I saw one of the lead developers say that 90% of the reported problems currently are caused by power issues, not the kernel code itself. If you want to experiment with using a cheap external PSU: http://modtown.co.uk/mt/article2.php?id=psumod FYI: Sata apparently does not have a ground on its cable, so you don't have to worry about ground loops. This too is just repeating what I've read on the lkml list, so check it out yourself if your curious. Greg -- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org