From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Stirling Subject: Re: Solaris ZFS on Linux [Was: Re: the " 'official' point of view"expressed by kernelnewbies.org regarding reiser4 inclusion] Date: Wed, 02 Aug 2006 00:50:49 +0100 Message-ID: <44CFE8D9.9090606@mauve.plus.com> References: <20060731175958.1626513b.reiser4@blinkenlights.ch> <200607311918.k6VJIqTN011066@laptop13.inf.utfsm.cl> <20060731225734.ecf5eb4d.reiser4@blinkenlights.ch> <44CE7C31.5090402@gmx.de> <5c49b0ed0607311621i54f1c46fh9137f8955c9ea4be@mail.gmail.com> <5c49b0ed0607311650j4b86d0c3h853578f58db16140@mail.gmail.com> <5c49b0ed0607311705t1eb8fc6bs9a68a43059bfa91a@mail.gmail.com> <20060801010215.GA24946@merlin.emma.line.org> <44CEAEF4.9070100@slaphack.com> <44CED95C.10709@slaphack.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com In-Reply-To: <44CED95C.10709@slaphack.com> List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: David Masover Cc: David Lang , Nate Diller , Adrian Ulrich , "Horst H. von Brand" , ipso@snappymail.ca, reiser@namesys.com, lkml@lpbproductions.com, jeff@garzik.org, tytso@mit.edu, linux-kernel@vger.kernel.org, reiserfs-list@namesys.com David Masover wrote: > David Lang wrote: > >> On Mon, 31 Jul 2006, David Masover wrote: >> >>> Oh, I'm curious -- do hard drives ever carry enough >>> battery/capacitance to cover their caches? It doesn't seem like it >>> would be that hard/expensive, and if it is done that way, then I >>> think it's valid to leave them on. You could just say that other >>> filesystems aren't taking as much advantage of newer drive features >>> as Reiser :P >> >> >> there are no drives that have the ability to flush their cache after >> they loose power. > > > Aha, so back to the usual argument: UPS! It takes a fraction of a > second to flush that cache. You probably don't actually want to flush the cache - but to write to a journal. 16M of cache - split into 32000 writes to single sectors spread over the disk could well take several minutes to write. Slapping it onto a journal would take well under .2 seconds. That's a non-trivial amount of storage though - 3J or so, 40mF@12V - a moderately large/expensive capacitor. And if you've got to spin the drive up, you've just added another order of magnitude. You can see why a flash backup of the write cache may be nicer. You can do it if the disk isn't spinning. It uses moderately less energy - and at a much lower rate, which means the power supply can be _much_ cheaper. I'd guess it's the difference between under $2 and $10. And if you can use it as a lazy write cache for laptops - things just got better battery life wise too.