Date: Wed, 18 Dec 2019 09:31:29 -0700 From: Alan Somers <asomers@freebsd.org> To: Karl Denninger <karl@denninger.net> Cc: FreeBSD <freebsd-stable@freebsd.org> Subject: Re: ZFS and power management Message-ID: <CAOtMX2ih%2BboayqOTCO95WT0WbYRdoxYgzYt%2B%2BGxTCoUYMS6ejA@mail.gmail.com> In-Reply-To: <57da15d4-0944-982b-7d7e-d7b2571e869c@denninger.net> References: <57da15d4-0944-982b-7d7e-d7b2571e869c@denninger.net>
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On Wed, Dec 18, 2019 at 9:22 AM Karl Denninger <karl@denninger.net> wrote: > I'm curious if anyone has come up with a way to do this... > > I have a system here that has two pools -- one comprised of SSD disks > that are the "most commonly used" things including user home directories > and mailboxes, and another that is comprised of very large things that > are far less-commonly used (e.g. video data files, media, build > environments for various devices, etc.) > > The second pool has perhaps two dozen filesystems that are mounted, but > again, rarely accessed. However, despite them being rarely accessed ZFS > performs various maintenance checkpoint functions on a nearly-continuous > basis (it appears) because there's a low level, but not zero, amount of > I/O traffic to and from them. Thus if I set power control (e.g. spin > down after 5 minutes of inactivity) they never do. I could simply > export the pool but I prefer (greatly) to not do that because some of > the data on that pool (e.g. backups from PCs) is information that if a > user wants to get to it it ought to "just work." > > Well, one disk is no big deal. A rack full of them is another matter. > I could materially cut the power consumption of this box down (likely by > a third or more) if those disks were spun down during 95% of the time > the box is up, but with the "standard" way ZFS does things that doesn't > appear to be possible. > > Has anyone taken a crack at changing the paradigm (e.g. using the > automounter, perhaps?) to get around this? > > -- > Karl Denninger > karl@denninger.net <mailto:karl@denninger.net> > /The Market Ticker/ > /[S/MIME encrypted email preferred]/ > I have, and I found that it wasn't actually ZFS's fault. By itself ZFS wasn't initiating any background I/O whatsoever. I used a combination of fstat and dtrace to track down the culprit processes. Once I had shutdown/patched/reconfigured each of those processes, the disks stayed idle indefinitely. You might have success using the same strategy. I suspect that the automounter wouldn't help you, because any access that ought to "just work" for a normal user would likewise "just work" for whatever background process is hitting your disks right now. -Alan
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