On Fri, Mar 26, 2010 at 01:27:17PM -0700, Peter Kieser wrote: > The 4096-byte sector drives work fine with mdadm. The main problem > you are going to run into with the WDC Green drives is their 8 > second "idle" setting. After 8 seconds, by default, the drive > parks its heads. This can lead to an amazingly high Load Cycle > Count (LLC) after just a month of operation due to the fact that > most disk access happens around that time causing the drive to > park and unpark in repeated cycles. For what it's worth... that head parking feature actually saves a measurable amount of power. On my system, with four drives, there is about a 10 watt (AC) difference between all four heads parked and all four heads non-parked. This finding is consistent with the power numbers suggested by SilentPCReview's reviews of these drives. > To fix this, find a utility called wdidle3 (I have it, if you are > unable to locate it) and set the idle timeout on the drives to 300 > seconds. These drives do not support TLER, there is no ability to > set it via firmware anymore - WDC removed this ability sometime > last year. This will prevent the rapidly increasing Load Cycle Count SMART counter. However, in my opinion, it also removes a useful power-saving feature of these drives. In other words, my system is mostly idle; I want the heads to be parked the majority of the time. Instead, without the wdidle3 hack, they constantly park/unpark despite an otherwise idle system. Here's the problem I've been unable to solve: if my system is truly idle for, say 10 minutes, then why don't my heads stay parked for 10 minutes? It appears that the heads will park, then five minutes later, *something mysterious* will cause them to unpark. I did some experimenting with this several months ago. See the list archives for August 20, 2009, subject "linux disk access when idle"[1]. As far as I can tell, I disabled every single daemon on my system, but still could not get the heads to park for more than five minutes. My point in all this is: I'd rather tune my software (Linux) to work better with my hardware, rather than remove what I consider to be a useful power-saving feature. I haven't re-visisted this in a while, but last time I tried, I couldn't find the guilty daemon or kernel setting responsible for the constant head un-parking. [1] http://marc.info/?l=linux-raid&m=125078611926294&w=2 -Matt -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
