Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1160998AbWHAE4a (ORCPT ); Tue, 1 Aug 2006 00:56:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161007AbWHAE4a (ORCPT ); Tue, 1 Aug 2006 00:56:30 -0400 Received: from warden-p.diginsite.com ([208.29.163.248]:33492 "HELO warden.diginsite.com") by vger.kernel.org with SMTP id S1160998AbWHAE43 (ORCPT ); Tue, 1 Aug 2006 00:56:29 -0400 Date: Mon, 31 Jul 2006 21:53:55 -0700 (PDT) From: David Lang X-X-Sender: dlang@dlang.diginsite.com To: David Masover cc: 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 Subject: Re: Solaris ZFS on Linux [Was: Re: the " 'official' point of view"expressedby kernelnewbies.org regarding reiser4 inclusion] In-Reply-To: <44CED95C.10709@slaphack.com> Message-ID: 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-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3506 Lines: 74 On Mon, 31 Jul 2006, 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. which does absolutly no good if someone trips over the power cord, the fuse blows in the power supply, someone yanks the drive out of the hot-swap bay, etc. >> now, that being said, /. had a story within the last couple of days about >> hard drive manufacturers adding flash to their hard drives. they may be >> aiming to add some non-volitile cache capability to their drives, although >> I didn't think that flash writes were that fast (needed if you dump the >> cache to flash when you loose power), or that easy on power (given that you >> would first loose power), and flash has limited write cycles (needed if you >> always use the cache). > > But, the point of flash was not to replace the RAM cache, but to be another > level. That is, you have your Flash which may be as fast as the disk, maybe > faster, maybe less, and you have maybe a gig worth of it. Even the bloatiest > of OSes aren't really all that big -- my OS X came installed, with all kinds > of apps I'll never use, in less than 10 gigs. > > And I think this story was awhile ago (a dupe? Not surprising), and the > point of the Flash is that as long as your read/write cache doesn't run out, > and you're still in that 1 gig of Flash, you're a bit safer than the RAM > cache, and you can also leave the disk off, as in, spinned down. Parked. as I understand it flash reads are fast (ram speeds), but writes are pretty slow (comparable or worse to spinning media) writing to a ram cache, but having a flash drive behind it doesn't gain you any protection. and I don't think you need it for reads >> external battery backed cache is readily available, either on high-end raid >> controllers or as seperate ram drives (and in raid array boxes), but >> nothing on individual drives. > > Ah. Curses. > > UPS, then. If you have enough time, you could even do a Software Suspend > first -- that way, when power comes back on, you boot back up, and if it's > done quickly enough, connections won't even be dropped... remember, it can take 90W of power to run your CPU, 100+ to run your video card, plus everything else. even a few seconds of power for this is a very significant amount of energy storage. however, I did get a pointer recently at a company makeing super-high capcity caps, up to 2600F (F, not uF!) in a 138mmx tall 57mm dia cyliner, however it only handles 2.7v (they have modules that handle higher voltages available) http://www.maxwell.com/ultracapacitors/index.html however I don't see these as being standard equipment in systems or on drives anytime soon David Lang - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/