It looks like the IntelliPark feature on a Western Digital Caviar Green HDD can cause issues with OpenBSD, which can be fixed/mitigated by disabling IntelliPark.
About 6 months ago, I built myself a new amd64 machine. I decided to optimize for low wattage--reducing power costs and waste heat, increasing UPS runtime--and so I chose a single Western Digital Caviar Green HDD. Although these drives are intended/marketed for something more like nearline storage, according to bonnie++, the drive performed roughly as well as the 7200RPM PATA-100 2-drive mirror in my old machine. The machine I built, initially running 4.7/amd64, then 4.8/amd64 (both unmodified -RELEASE) was never stable for more than a couple of days at a time. The machine would freeze hard, sometimes with the HDD light lit solid, usually not. I worked around a number of bugs, trying a patched kernel with http://marc.info/?l=openbsd-misc&m=128897915014154&w=2, and disabling installing an fxp(4) so I could disable the onboard re(4). I wrote scripts to monitor hw.sensors, SMART, and various stats from systat(1), and graph them using rrdtool. What I noticed was that my machine would generally crash right before an IO-intensive cronjob started. I also noticed that SMART stat 193 (Load/Unload Cycle Count) was very high, and climbing rapidly. Doing some research on this stat, I found out that WD Caviar Green drives have a feature called IntelliPark that parks the HDD heads after 8 seconds of inactivity. This is supposed to make the HDD more efficient, but has been reported not to play well with Linux, and WD provides a workaround: the WDIDLE3 utility, which would allow me to change/disable the IntelliPark 8-second timeout. I ran WDIDLE3 on my WD Caviar Green HDD, setting the timeout to the maximum allowed (300 seconds). I have a monitoring process running that writes to disk roughly every 60 seconds, so IntelliPark is effectively disabled for me. As of now, the system has been up a record 19.5 days without issue. Disabling IntelliPark fixed the major freeze issue I was having. I don't know exactly what was going on, but it seems like the drive would get stuck in a state in which the head reloading had failed, or had not completed within a certain timespan, and the OS and the drive controller become deadlocked. Attempting to reproduce the problem is painful, both in terms of how long it can take to cause a freeze, and for the wearing out it did of the drive. I'm not sure if I should file this as a PR, or consider this a design flaw in the drive (or a consequence of "off-label" use) and just be content with the fix/workaround that I've found. If anyone has any recommendations, or any experiences with the Caviar Green drives, I'd like to hear them.
