From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: linux disk access when idle Date: Fri, 21 Aug 2009 18:00:43 -0400 Message-ID: <4A8F190B.9010406@tmr.com> References: <20090820163522.GA29215@sewage> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20090820163522.GA29215@sewage> Sender: linux-raid-owner@vger.kernel.org To: Matt Garman Cc: linux-raid List-Id: linux-raid.ids Matt Garman wrote: > The scope of this question is probably broader than Linux RAID, but > I thought I'd try here before going to the LKML... > > I have a fileserver/NAS box that has four Western Digital GreenPower > drives in software RAID-5 (i.e. Linux md). There was some noise > about these drives not too long ago: when used under Linux, they > tend to have really high (and rapidly increasing) SMART > Load_Cycle_Count values[1]. > > Basically, in order to save power, these drives park the read/write > heads after so many seconds of inactivity. According to > SilentPCReview[2], the 1 TB model uses 5.7W when idle and only 3.7W > when the heads are unloaded. Apparantly, each head parking event > causes teh Load_Cycle_Count value to increase. > > Most people seek to disable this head parking behavior to stop that > Load_Cycle_Count value from growing alarmingly high. I actually > want to use it to it's full potential. > > I've got a Kill-A-Watt electricity meter connected to my NAS box. I > see a difference of 10 watts power usage when the heads park (I can > hear them unload, so I know when it happens). Allowing for some > power supply inefficiency, I'd say my observation is consistent with > SPCR's numbers. > > The problem is, the drives don't stay in this parked state very > long. I haven't actually timed the state changes, but average power > consumption over a long time (e.g. a week or more) is at the higher > (i.e. +10) level. > > So I figure, something is accessing these drives shortly after the > heads park, causing them to un-park (and increasing power > consumption). But this machine is idle 95% of the time. And even > then, the overwhelming majority of the accesses are reads, with very > few writes (literally, a handful of writes per week). > > /proc/sys/vm/dirty_expire_centisecs still set to 30 sec? > So what I'm trying to figure out is, what is causing the disk > access? It could be any one of: > > - Kernel > - RAID subsystem (i.e. md) > - XFS filesystem > - NFS > - Samba > - ??? > > I'm hoping someone has enough knowledge of these systems to point me > in the right direction for tuning things. The goal is that when the > machine is idle, it is "truly" idle, meaning, no disk accesses take > place and the heads can stay parked (thus saving energy). > > Thank you, > Matt > > LINKS: > [1] http://groups.google.com/group/linux.kernel/browse_thread/thread/505ccf760023d132/7e4f4e996f911efd > > [2] http://www.silentpcreview.com/article804-page2.html > > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- bill davidsen CTO TMR Associates, Inc "You are disgraced professional losers. And by the way, give us our money back." - Representative Earl Pomeroy, Democrat of North Dakota on the A.I.G. executives who were paid bonuses after a federal bailout.