Posts by ilmari
19 posts • joined Thursday 18th October 2012 12:58 GMT
Availability
Couldn't agree more on the availability comment. What's the point of having netflix or other services, when all they have is movies you've already seen... on VHS.
I didnn't attempt to read the paper, the quoted bits were enough to put me off.
Speaking of bits, I do remember some sysadmin stating a couple of years ago, that rebuilding a degraded raid5 error is essentially poinless, and the best course of action is to restore from your backup onto a fresh array.
The argument was, that if you look at the expected bit error rates of a harddrive, and compare it to the size of your array, you'll discover you're statistically likely to encounter atleast one flipped bit during raid rebuild, and end up with corrupted data, in one file, somewhere.
As I'm a mere caveman studying the entrails of a wooly mammoth, I must admit I'm just speculating when I propose the theory, as told to me by the mammoth's internals, that perhaps these researchers are presenting error correction codes, and placement strategies for these codes, that would push the probability of single bit errors up into the realm of "wont happen" for another decade or so?
Re: So..
Current comercially available technology is roughly on the order of a D sized lithium-ion battery being able to start a petrol car engine. That's not capacity or energy though, it's power. The Energy in a Li-ion like that is about the same as in the much smaller (by dimensions and weight) battery in your phone.
As for 3D electrodes, Edison invented a similar thing for the Edison battery. If I've understood (and remembered) correctly, he made thin sheets of material, which he then shredded coated onto thin sheets, which were shredded and coated onto sheets, repeated until he arrived at a sheet with a total surface area several orders of magnitude larger than the dimensions as measured by a ruler :)
Oh dear god, please no
Now everyone will be blaming memory effect for everything
... "I installed 50 background apps, but only 49 of them use gps and 3g, and I'm not sure about the 50th, what's a bitcoin miner do? Anyway, now my battery doesn't last anymore??? Can't be the apps, must be memory effect!!"
... "I left my phone empty in a drawer for a month after I droppped phone in beer, and now battery life sucks. I opened up the phone and attached the battery to a car battery charger for a week, but that didn't help, so I borrowed a medical defibrillator and gave the battery repeated shocks, but memory effect is just getting worse and worse, halp!"
In all seriousness though, if you take someone very familiar with typical Li-Ion batteries such as LiCoO2 and similar, which we have in phones and computers, and tell them LiFePo4 is "just like" LiCoO2 but explosion-proof and lower voltage. it takes just one charge cycle for them to discover that LiFePo4 behaves nothing like traditional LiCoO2. When I first got a LiFePo4 batterypack I immediately noticed that charge behaviour was quite different. I couldn't find much litterature on the subject, except vague nonsense about "forming charge", and a somewhat competent looking research paper that used xray microscopy to compare slowcharged batteries to fastcharged batteries (where fast was on the order of 10 minutes), the findings being that fast charge caused less wear and tear.
Anyway, the point being that there's only one laptop ever (OLPC), and no phones at all, that have used a LiFePo4 battery. Considering how different LiFePo4 is from what's actually used in laptops and phones, this memory effect is entirely irrelevant for the normal user, even if the discovered effect wa s bigger than 1/1000th..
1/1000th is ldudicrously small anyways, considering battery meters in phones andsuch often are off by 20 percent or more... That also means it's nearly impossible for regular users to draw any meaningful conclusions from how they charge and use their devices, as there's no accurate measurement of drain and charge level, and the zero-point often jumps around from cycle to cycle.. Zero-point being the charge level at which the phone considers itself empty..
Unboxing?
Come on, where's the unboxing video?1
The new unboxing experience (*puke*) sounds like more important news than the actual contents in the box, which was fairly uninteresting.. :)
Imagine if intel shipped this strapped to a pallet, they'd beat HP's record :)
How do you implement these kinds of rules? You need to get them far enough upstream so that your links don't get saturated, but the further up you go the more reluctant the admins become of doing any filtering.
As for spamhaus itself using dns this or that, it's wholly irrelevant to whether they'd be vulnerable to this attack or not. They'd be just as vulnerable to this attack if they had 0 computers, 0 servers and 0 services on offer on their line.. their line would still get saturated by the traffic.
The sun is a massively parallell random number generator, it'd suck if there was a hashsum collision
Radiation sources
It's odd how nobody complains about increased cancer levels near coal fired powerplants, when they emit more radiation than nuclear powerplants. :)
The difference, I guess, is that everybody knows radiation is produced in large amounts in nuclear powerplants (and contained within), whereas fewer people are aware of the continous emission of low level radiation from coal powerplants. :)
Posted in Boeing outlines fix for 787 batteries
Re: insulation/electrical tape
Individual voltage monitors per cell is an absolute must!! Without that capability, the cells WILL drift apart over time, and one cell will get overdischarged or overcharged.
NiMH, NiCd and Pb batteries tolerate overcharge (within reason), so those packs ae always slightly overcharged, to ensure that the individual cells stay balanced. LiIon has zero tolerance for both overcharge and overdischarge. When charging, individual cells must all be monitored, if a cell reaches max voltage beforr others, the battery management system must tell the charger to slow down, and also start draining power away from that cell.
Without this, the batterypack is a ticking timebomb.
DRAM cache is what the OS does. Throw in the preload utility, and the kernel will get hints to use idle I/O time to preread in disk contents. I wish it could go further than just reading in executables and libraries though, if it senses you've got ludicrous amounts of ram.
As for execute-in-place (XIP), due to the block nature of nand flash, xip only works on NOR flash, which is horribly expensive and doesn't exist in anything with a faster cpu than your fancy wristwatch.
I imagine a "live usb key"-on-ssd approach might work. Squashfs image of the OS, initrd script to preload all of that into ram at startup, in one sequential chunk and not in random order. Optional "persistence" mode, where saved files, changed settings, etc get added to a ext4/btrfs/f2fs partition.. The latter will of course slow you back to traditional ssd level of runtime performance..
I'm more annoyed with applications today than operating systems. On your regular sd card or usb flash, the amount of I/O that, for example, clicking back in firefox causes is about 2 seconds of I/O busy... Why? Because databases. Everything is a database these days, and databases go to great lengths to ensure that data is on disk NOW, RIGHTAWAY, and that data is written so that no corruption or loss occurs if power is lost or drive yanked in the middle of that write. This is the perfect recipie to defeat every I/O reducing, optimizing and make-go-faster algorithms that operating systems have.
Some people might care if a website cookie was lost, or that the visited/not-visited status of a link is comitted to disk within 1ms of you clicking the link.. Personally I'm not that fussy. Sometimes when running from usb live keys, I just copy and symlink the dot-mozilla directory to tmpfs (ramdisk) before starting firefox, and copy it back once I exit firefox. That means I avoid sqlite's disk-abusing tendencies, but with the risk that the entire browser session's history, cookies and saved forms/passwords data is lost to the state it was in before starting firefox.
I have a feeling there should be some middle ground between the default extreme, and my hacked together extreme.
People tell me windows has largely started to ignore requests made by apps wanting to commit data to disk immediately.. I guess they must have a new api for things that /really/ do want/need it.. Soon enough every app catches on to the new way of doing things, and we're back at slow I/O, and have to ignore requests through the new API, and create a new new API for things that really really want it. Sigh.
Standby times are pretty good as is, power consumption is on the order of 5mA in standby, including 3g standby. This gives you a standby battery life of over a week.. Improving that to 2 weeks or 4 weeks with same battery sounds fantastic, but...
The issue is that the amount of time our devices spend in standby is very low. There's stuff constantly updating in the background for no good reason, and the controls available to the user is poor.. Every widget and app seems to think they're special, that they can ignore being a good citizen because the user installed it they must have the right and obligation to constantly update their UI, data and what not, even if user hasn't used or looked at it all day..
Even if standby power use could be reduced to 0, we'd still not get more than the day or two of battery life..
Re: I'd look at the Battery Power Conditioning Circuits
I agree, mostly because I find it hard to believe a japanese company like GS Yuasa would make substandard battery cells.
Li-Ion at too low voltage or too high voltage will start producing metallic lithium (highly volatile), or starts dissolving the copper current collectors into the electrolyte. This dissolved copper then becomes metallic again when battery voltage is restored to safe levels, and the copper might have formed thin strands acting as shunts. Current across those can locally heat up the cell sufficiently to set off thermal runaway (iirc the required temperature is slightly above 100C). Think of it as chemically "growing" an ignition wire into the insides...
When having multiple cells, each cell must be individually monitored to stay within prescribed voltage limits. In order to not get the entire pack limited by the lowest voltage cell and highest voltage cell, you need some sort of system that either adds more charge to the lowest cell, or removes power from the highest cell. Removing from the highest cell is the most common practice. Then you need to design this balancing system so that it fails in a safe way. Many electrical vehicle hobbyists have been bitten by this, their electronics have failed and a single battery cell has been drained totally dead. Trying to either charge or discharge that pack will then most likely cause a fire.
The charging system needs feedback from this balancing system, so that the charging system doesn't charge faster than the balancing system can remove charge from the highest cell(s). Without that feedback, there'll be atleast one cell that gets overvolted for a brief period of time. The damage accumulates (you can't just say "oops, but it didnt blow up this time, so it's ok")
Same applies to discharge portion, must cease discharging when the lowest cell reaches lowest permissible voltage. Using the pack voltage for this purpose will lead to problems.
I've seen a surprising amount of highly skilled electrical and electronics engineers that have absolutely no clue about batteries, they would blow up a Li-Ion pack quite quickly with the battery management they'd design. Alot of EEs seem to treat batteries as some sort of black boxes that work as electronic fuel tanks and manage themselves. I guess it makes sense, they're electronics people not chemistry people.. Wouldn't surprise me if the problem can be traced back to the battery management system...
Re: battery cooling
I've been wondering about thermal management in that bay, is it pressurized, if not, how does thinner air affect the thermal management?
Posted in Linksys vuln: Cisco responds
legendary
My WRT54GL just wont die. Lighning storms have made the outlet it's connected to spew out fire and sparks, two summers in a row. Each time I just replaced the wallwart. The second time it happened I got a surge protector, which helped the situation in that every other outlet started spitting fire.
Losing the wallwart isn't even that big of a deal even for the internet addict, WRT54GL isn't too fussy about power, will run off of almost anything, the battery in your smoke detector (a minute or two), the batteries in that 80s boombox you still havent thrown out, or even a car battery will do, enough to tide over the addiction until the shops open and you can get new wallwart..
hate couriers
I hate couriers for this reason, charging you 50 bucks to talk with customs when it would take yourself about 5 minutes to handle the matter online on the customs website..
The traditional post system works better, they ask you for permission to deal with customs, you tell them "No, thanks, I'll do it myself", and it costs you nothing. As a bonus shipping rates are a tenth of couriers, even with tracking and insurance added.
This is nothing new
On Nokia's page describing Xpress Browser, even before recent media coverage, was a full screen picture with boxes and arrows showing data goes through Nokia, gets modified and optimized, and sent back to user.
As for "lawful intercept" capabilities, all you need is Verisign or other authority trusted by the suspects' browsers sign ssl certificates on the fly (or indeed lend you a signing key), take that capability to isp and have them redirect traffic through your own systems. SSL is totally inadequate for authenticating the source and destination, when the system of doing that relies on entities techincally capable of lying, and compellable to do so by people with big guns and the right to bear taxes.
Not the first rats to leave the ship.. When elop came aboard, intel, hp, samsung and others launched an aggressive hiring campaign. Even random members of the Maemo/MeeGo USER community got aggressively solicited to come work for hp and others...
Not mourning
The A123 batteries were superb. Recharge in 8 minutes, brutal power density and practically indestructible.
However, if you wanted to buy batteries and you didn't want to buy one billion batteries, they gave you the finger.
People were buying the powertool battery packs, breaking them up to get the A123 cells inside, which was both expensive and increasingly unreliable when inside the packs you suddenly found some other crap and not the coveted A123 cells...
Meanwhile, while A123 has been flipping the bird to customers, the chinese manufacturers have improved their products to the point where they have 1/20th to 1/10th of the power of A123, which is "good enough" for electric cars if you accept overnight charging. Unlike A123, the chinese companies are happy to sell their products both to distributors and to individuals who order a prius' worth of batteries.
