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Date: Tue, 01 Aug 2006 00:59:22 -0500 From: David Masover <ninja@...phack.com> To: David Lang <dlang@...italinsight.com> CC: Nate Diller <nate.diller@...il.com>, Adrian Ulrich <reiser4@...nkenlights.ch>, "Horst H. von Brand" <vonbrand@....utfsm.cl>, ipso@...ppymail.ca, reiser@...esys.com, lkml@...productions.com, jeff@...zik.org, tytso@....edu, linux-kernel@...r.kernel.org, reiserfs-list@...esys.com Subject: Re: Solaris ZFS on Linux [Was: Re: the " 'official' point of view"expressedby kernelnewbies.org regarding reiser4 inclusion] David Lang wrote: > On Mon, 31 Jul 2006, David Masover wrote: >> 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. Power supply fuse... Yeah, it happens. Drives die, too. This seems fairly uncommon. And dear God, please tell me anyone smart enough to set up a UPS would also be smart enough to make tripping over the power cord rare or impossible. My box has a cable that runs down behind a desk, between the desk and the wall. Power strip is on the floor, where a UPS will be when I get around to buying one. If someone kicks any cable, it would be where the UPS hits the wall -- but that's also behind the same desk. > 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 Does gain you protection if you're not using the RAM cache, if you're that paranoid. I don't know if it's cheaper than RAM, but more read cache is always better. And losing power seems a lot less likely than crashing, especially on a Windows laptop, so it does make sense as a product. And a laptop, having a battery, will give you a good bit of warning before it dies. My Powerbook syncs and goes into Sleep mode when it runs low on power (~1%/5mins) >>> 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. Suspend2 can take about 10-20 seconds. It should be possible to work out the maximum amount of time it can take. Anyway, according to a quick Google search, my CPU is more like 70W. Video card isn't required on a server, but you may be right on mine. I haven't looked at UPSes lately, though. I need about 3 seconds for a sync, maybe 10 for a suspend, so to be safe I can say for sure I'd be down in about 30 seconds. So, another Google search, and while you can get a cheap UPS for anywhere from $10 to $100, the sweet spot seems to be a little over $200. $229, and it's 865W, supposedly for 3.7 minutes. Here's a review: "This is a great product. It powers an AMD 64 3200+ with beefy (6800GT) graphics card, 21" CRT monitor, secondary 19" CRT, a linux server, a 15" CRT, Cisco 2800XL switch, Linksys WRTG54GS, cable modem, speakers, and many other things. The software says I will get 9 minutes runtime with all of that hooked up, realistically it's about 4 minutes." This was the lowest time reported. Most of the other reviews say at least 15 minutes, sometimes 30 minutes, with fairly high-end computers listed (and monitors, sometimes two computers/monitors), but nowhere near as much stuff as this guy has. I checked most of these for Linux support, and UPSes in general seem well supported. So yes, the box will shut off automatically. On a network, it shouldn't be too hard to get one box to shut off all the rest. It's a lot of money, even at the low end, but when you're already spending a pile of money on a new computer, keep power in mind. And really, even 11 minutes would be fine, but 40 minutes of power is quite a lot compared to less than a minute of time taken to shut down normally -- not even suspend, but a normal shut down. I'd be tempted to try to ride it out for the first 20 minutes, see if power comes back up... > 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 This seems to be a whole different approach -- more along the lines of in the drive, which would be cool... - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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