Tracking Down a Single-Bit RAM Error 277
Hanji writes "We have discussed here before the potential effects of and protections against cosmic ray radiation, but for the average computer user, it's an obscure threat that doesn't affect them in any real way. Well, here's a blog post that describes a strange segfault and, after extensive debugging, traces it down to a single bit flip, probably caused by a stray cosmic ray. Lots of helpful descriptions of Linux debugging techniques in this one, and a pretty clear demonstration that this can be a real problem. I know I'm never buying a desktop without ECC RAM ever again!" The author acknowledges that it might not have been a cosmic ray-based error, but the troubleshooting steps are interesting no matter what the cause.
Ugh, single bit errors (Score:3, Interesting)
One of my computers had an intermittent failure in a RAM chip/line/something somewhere that mostly manifested as SHA/MD5 failures when I was checksumming large files that I'd downloaded. Never showed up in Memtest86, but eventually I eliminated every other possibility. IIRC, I solved it by underclocking the machine and then replacing it when I was able.
Cosmic rays, my ass. Occam's Razor time. (Score:5, Insightful)
You are on the right track. As someone with over a quarter century of background in combined embedded software and hardware design (the most recent decade for life-dependant systems), it always amazes me how quickly pseudo-technical people jump to wild speculation for observations that they cannot explain.
They fail to understand that a hardware system is an imperfect representation of the theory (probably the biggest failure in the schooling of software developers and even some hardware is to get this message into their heads). While they feel comfort in the theory of a binary system, they utterly fail to understand that our real systems, like us, are imperfect and, like us, live in an analog world. Simple things like temperature variations, noise from common (rather than cosmic) sources, marginal design timing, imperfect components, simple intermittents, etc., are 10^24 times more likely the cause.
But they're not as fascinating as wild speculation, are they?
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Not only that, but they are also systems we can only approach from a very abstract perspective when it comes to debugging. Our options to debug complex hardware are very abstract, inaccurate, and incomplete.
Single bit errors (Score:3, Interesting)
This turned out to be a manufacturing problem wit
Re:Cosmic rays, my ass. Occam's Razor time. (Score:5, Interesting)
On the subject of the imperfect nature of machines, I found this post by Richard D. James (aka Aphex Twin, a noted electronic music composer) quite interesting. He describes how the physical machinery of analog electronic music machines means it is near impossible to duplicate them in digital programs.
link [archive.org]
Author: analord
Date: 02-07-05 03:14
some people bought the analogue equipment when it was unfashionable and very cheap though.
some of us are over 30 you know!
anyone remember when 303`s were £50? and coke was 16p a tin? crisps 5p
also you have overlooked A LOT of other points because its not all about the overall frequency response of the recording system its how the sound gets there in the first place.
here are some things which you can`t get from a plugin,they are often emulated but due to their hugely complex nature are always pretty crass aproximations..
the sound of analogue equpiment including EQ, changes very noticably over even a few hours due to temperature changes within a circuit.
Anyone who has tried to make tracs on a few analogue synths and make them stay in tune can tell you this,you leave a trac running for a few hours come back and think Im sure I didnt fucking write that,I must be going mental!
this affects all the components in a synth/EQ in an almost infinte amount of tiny ways.
and the amount differs from circuit to circuit depending on the design.
the interaction of different channels and their respective signals with an analogue mixer are very complex,EQ,dynamics....
any fx, analogue or digital that are plugged into it all have their own special complex characteristics and all interact with each other differently and change depending on their routing.
Nobody that ive heard of has even begun to start emulating analogue mixer circuitry in software,just the aesthetics,it will come but im sure it will be a crap half hearted effort like most pretend synth plugins are.
they should be called PST synths, P for pretend not virtual.
Every piece of outboard gear has its own sound ,reverbs,modulation effects etc
real room reverb, this in itself companies have spent decades trying to emulate and not even got close in my opinion, even the best attempts like Quantec and EMT only scratch the surface.
analogue EQ is currently impossible in theory to be emulated digitally,quite intense maths shit involed in this if youre really that interested,you could look it up...good luck.
your soundcard will always make things sound like its come from THAT soundcard..they ALL impose their different sound characteristics onto whatever comes out of them they are far from being totally neutral devices.
all the components of a circuit like resistors and capacitors subtley differ from each other depending on their quality but even the most high quality milatary spec ones are never EXACTLY the same.
no two analogue synths can ever be built exactly the same,there are tiny human/automated errors in building the circuits,tweaking the trimpots for example which is usually done manually in a lot of analogue shit.
just compare the sound of 2 808 drum machines next to each other and you will see what I mean,you always thought an 808 was an 808 right?
same goes for 303`s they all sound subltey different,different voltage scaling of the oscillator is usually quite noticable.
VST plugins are restricted by a finite number of calculations per second these factors are WAY beyond their CURRENT capability.
Then there is the question of the physicallity of the instrument this affects the way a human will emotionally interact with it and therfore affect what they will actually do with it! often overlooked from the maths heads,this is probably the biggest factor I think.
for example the smell of analogue stuff as well as the look of it puts y
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It was me.
Sorry 'bout that.
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Electronics are designed well within tolerances for temperature and EM interference. At least, good ones are. Since my fans are broken, I've been running the GPU in my Thinkpad to 107C every day for a few years when I play games. No problems yet.
As someone who hasn't been in school in 30 years, memory loss, sits on the porch with a shotgun hollering at kids, has to call his grandson to install the newfangled Norton Internet Security because you've been
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Although interesting, TFA it is without a doubt the most pedantic and roundabout way I've ever read of establishing your rig is not stable.
From TFSA:
And in fact, since that incident, I've had several other, similar problems. I haven't gotten around to memtesting my machine, but that does suggest I might just have a bad RAM chip on my hands.
Yeah he has a stuck or semi-stuck bit and a hour or two of his life he won't get back.
In such a circumstance I'
Re:Ugh, single bit errors (Score:4, Informative)
This may have been true at one time, but ECC RAM is no longer that expensive. I just looked at prices on Newegg:
8 GB DDR3 $214.99
8 GB DDR3 ECC $274.99
In some cases, depending on the brand and the speed, ECC is actually *CHEAPER*.
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You'll also need a consumer-level motherboard with ECC support. Which are not common, which means you'll be stuck with a server-grade motherboard which costs more, has potential to change: cpu compatibility, case compatibility, and features on the board itself.
There's alot more to making the change from non-ECC to ECC than just swapping out your ram.
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You'll also need a consumer-level motherboard with ECC support. Which are not common, which means you'll be stuck with a server-grade motherboard
Or, you know, go AMD. Because they don't limit ECC to only server parts.
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Or, you know, go AMD. Because they don't limit ECC to only server parts.
Or, just buy any one of a half-dozen motherboards costing less than $200 [newegg.com] and add a Xeon [newegg.com] that is priced within 5% of the equivalent spec non-Xeon.
Sure, these might not be the best motherboards for gaming (although they are pretty competitive compared to other socket 1156 motherboards), but for a workstation doing everything else, they're great.
And, this way you get a motherboard that is thoroughly tested with ECC RAM (as that's what is expected to be used), and likely far better BIOS control of the ECC.
Re:Ugh, single bit errors (Score:4, Interesting)
I think the original article showed why you'd want ECC in a desktop machine -- random bit errors do happen in real life. I don't see how a warranty makes this less of an issue -- if my machine silently corrupts data due to a bit error, getting a $50 replacement DIMM isn't really going to satisfy me. Does ECC really cost 5X over non-ECC?
If he was processing data or editing a spreadsheet, then that bit error could have corrupted his data. If he was compiling a program for distribution (perhaps to thousands of machines), that bit error could have corrupted his executable, causing errors on all of the machines it was deployed to.
After reading this article, the question that comes to mind is why am I *not* running ECC on my desktop?
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Re:Ugh, single bit errors (Score:5, Insightful)
I'm not sure why you'd want ECC ram in a desktop, unless it's some sort business critical machine that you're willing to spend 5 or 6 times what a normal desktop costs. For day to day use, ECC is overkill.
My desktop has 8GB of ECC in it. This cost I think $40 more than non-ECC, and meant I got an Althon II x4 instead of a Core i5. That "5 or 6 times what a normal desktop costs" is either bullshit or Intel-onlyism (which is just another kind of bullshit).
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Have a look at Mac Pro ram options for 8 gb.
http://eshop.macsales.com/shop/memory/Mac-Pro-Memory#1066-memory [macsales.com]
Re:Ugh, single bit errors (Score:4, Informative)
Depends on the type of desktop. ECC these days doesn't cost much more than non-ECC... Dell and HP may not want to admit it, but I buy ECC DDR3 all the time as I build a lot of white-box servers, and frankly even the lamest "gaming" Ram carries a higher premium than ECC.
The tricky thing is that while most (all?) current AMD boards can take ECC ram (unbuffered, not registered), no consumer Intel boards can handle ECC - you need to step up to a Xeon processor and chipset. Luckily the single-processor setups don't cost all that much more than their mid-range consumer equivalents, but you do have to sacrifice buzzy features like USB 3.0, SLI/Crossfire, eSATA and overclocking. One exception to this is the EVGA Classified SR-2, which has absolutely everything, but it's $600 and requires a special oversized chassis (or a lot of dremel work).
I'm going to put this out there: if someone is genuinely concerned about bit errors to a degree where the loss of work due to a minor crash or reboot is significant enough, go ahead and spend an extra 10% on ECC. Even if you pack that board with 96gb of memory, it's still cheaper than six months of therapy and thorazine :P
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One off single bit flips DO happen in otherwise perfectly good hardware.
I saw one years ago. A '386 running a single batch process (under DOS). It was supposed to be a massive sorting operation (500MB was a lot back then) and the results came out terribly scrambled. Each entry was fine except that they were not in order as they should have been. Since it was a batch I had the luxury of running it again. The error NEVER repeated. The same machine ran flawlessly for the rest of it's natural life after passing
ask Voyager 2 program managers (Score:2)
Takes me back (Score:5, Interesting)
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There's a Redmond joke in here somewhere. Regardless, I'm going to start blaming all my typos on bitflips caused by cosmic rays.
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larger programs to fail too frequently
We showed him right, huh?
Easter Earthquake (Score:5, Interesting)
I don't know about cosmic rays, but immediately following the Easter day Earthquake in Guadalupe Victoria (about three hundred miles from where I was located) I tried to fire up my laptop and then my desktop, both of which had been suspended to RAM. Neither one would wake up, though the lappie displayed a garbled screen. No errors in the log files (Ubuntu 9.10 on the sys76 lappie, Deb Lenny on desktop).
Re:Easter Earthquake (Score:4, Insightful)
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RAM error? (Score:5, Interesting)
Forget a RAM error, I have seen a bit on a file on the disk flip.
After years of successful operation a Perl script quite working. On investigation a G was transformed to a W a difference of one bit. The file mod date was years old.
Re:RAM error? (Score:5, Interesting)
I experienced almost exactly that issue with a RAM error. My system was apparently stable, and then one day I got a syntax error in a system Perl script: one character had changed. The script was owned by root and otherwise untouched. After puzzling over it for quite a while I realized it could be a RAM error and ran memtest86. It reported a single permanently stuck bit in my 512MB of RAM. I found a kernel patch to manually mark problem RAM areas as reserved and kept on running with that RAM for a few years.
Are you sure that perl script issue was caused by a drive error? A RAM error can cause the same apparent problem, if the corruption happens in the kernel's cache. However, it shouldn't be permanent as it will not be written back to disk (the cache won't be dirty) unless someone actually modifies the file.
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Would the perl script be loaded at the same address in RAM every time? Wouldn't that likely be a one-time unrepeatable problem?
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The perl script will stay cached until something else pushes it out of RAM or until you reboot the system. In general, files are loaded once and stick around for quite a while unless you're low on RAM. In my case, it stayed cached while I investigated it, and I could see the broken character with various viewers. Bad RAM could also cause an intermittent issue if it happened to affect memory used by the Perl interpreter to load the file (that would change each time), but in this case it affected the kernel's
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Would the perl script be loaded at the same address in RAM every time? Wouldn't that likely be a one-time unrepeatable problem?
If the stuck bit was in the file cache, then it would be repeatable for as long as the script stayed cached, plus you could load the file up in a text editor and see the changed character, etc. Then it would mysteriously go away.
Also (Score:5, Informative)
Disks have a lot, and I mean a LOT of ECC on them. It is not a situation of "I need to write a 1 so I'll place one at this location on the drive." They use a complex encoding scheme so that bit errors on the disk don't yield data errors to the user.
Then there's the fact that bits aren't even stored as bits really. All current drives use (E)PRML which is (Enhanced) Partial Response Maximum Likelihood. What this means is bits aren't encoded as a high-low state or FM wave or any of that. They are written using flux reversals, but the level is not carefully controlled, it can't be. So when you read the data the drive actually looks at an analogue wave. It encodes the partial response it gets, and then finds the maximumly likely pattern that matches.
Sounds like voodoo but works really well. Things are not simple thresholds or the like, it is a complex system and ends up being quite robust and resilient to error.
So it is highly unlikely that you had a bit flipped on a disk. Would require some amazing circumstances to happen. The RAM error is far more likely. Not just the cosmic ray thing but, as the parent noted, bad RAM. Normally when RAM fails, it fails catastrophically and it is immediately apparent. Not always though. It can not only fail on single bit locations, but only during certian ops. That is why memtest does so many different tests. One kind might works fine, another might fail. Rare, but I've seen it on a few systems.
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However, single-bit errors are possible with faulty disk hardware. The cache RAM on the disk or its interface can be flaky, and for PATA disks a bad cable can cause single-bit errors. SATA disks usually catch IO errors since they use a more complicated encoding and make use of checksums.
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However, single-bit errors are possible with faulty disk hardware.
I'm sure you're right, but in this case there's essentially no way a disk hardware failure is going to cause the same bit to fail the same way, but no other bits fail.
In this case, I'd expect it's a bit flip in the OS disk cache.
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The bit fails while it is read from the disk, then persists in the OS cache. The end result is the same (a corrupted OS cache), but the cause is different, as the bit flipped before it ever made it to the cache.
Re:Also (Score:5, Funny)
I doubt this is true. The disk would have to be spinning at 88 mph in order to activate the flux capacitor, and the power brick would need to supply 1.21 gigawatts to the drive, which exceeds the capacity of even the most tricked-out gaming PC. I think you'd better check your science, my friend.
+1 Informative (Score:3, Funny)
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Been common with all kinds of things for some time. CD-ROMs, for example, use EFM, eight-to-fourteen modulation at their most base level. Eight logical bits are actually written as fourteen pits on the disc. Again the reason is error correction. They have more error correction at higher levels, and even more for data CDs. That's why data and audio CDs don't add up. An 80 minute CD holds 700MB of data. But do the math on 44.1kHz, 16-bit, 2-track audio and it takes 800MB of data to hold. Well in data mode the
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I'd second the idea of a filesystem error. I had a mystery error show up similar to what he described. Someone modified one of my files, only changing one character. I was the only one with access to the machine. I fixed it, and voila, problem solved. A few weeks later, filesystem errors started showing up in the system log. It was a failing drive, not just a dirty filesystem. It must have been cosmic radiation damaged the disk. :)
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How did you verify it was actually on the disk, and not read from disk cache in memory?
Disk sectors have CRC checksums on them, so it's just extremely unlikely the bits flipped on the physical medium. It seems even less likely the bit got flipped somehow that caused a write to disk (and your file mod date would suggest this was unlikely as well).
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Forget a RAM error, I have seen a bit on a file on the disk flip.
After years of successful operation a Perl script quite working. On investigation a G was transformed to a W a difference of one bit. The file mod date was years old.
Ditto, except it was something like a w to a 7.
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/*After years of successful operation a Perl script quite working*/
And a bit flipped to an e?
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Quit working? I'm surprised that didn't turn your perl script into pong.
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And 10,000 years from now, your Perl script has become the complete works of Shakespeare...
Ah, Grasshoppah (Score:2)
"What is the sound of one bit flipping?"
Or
"If a disk crashes in a server farm and there's no one there to hear it, does it make a sound?"
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It's not cosmic. It's from the die/package (Score:5, Informative)
Soft errors in DRAM are far more likely to be the result of alpha particle decay from materials in the die and packaging.
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Very old processed lead, such as that used for the roofs of some European cathedrals, has been used to build supercomputers since more of the radioactivity has decayed.
That sounds a bit fishy.
I _think_ I might be willing to believe the radioactivity of lead, presumably from contamination through some other source radioactive mineral in the ore that decays into radioactive lead. What I have a hard time believing though is that supercomputer makers wouldn't just use non-lead solder, which has been around for
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Never worked with lead-free solder have you?
It's only very recently that it's become practical for widespread use and it's still not settled how well it will work in applications that require maximum reliability. The problems with higher melting points, reduced wetting, tin whiskers, appropriate fluxes, etc. took a long time to sort out.
I'm sure that when a lot of early supercomputers were being built the components used would have been destroyed by the temperatures required to solder without lead.
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Maybe. It just sounds like an urban legend to me. I was also able to find a 25 year old patent claiming that gold-tin solder assured both high reliability in chip making.
http://www.google.com/patents/about?id=MZY1AAAAEBAJ&dq=4512950 [google.com]
Re:This would be important (Score:5, Interesting)
Billions of years in the ground, and only a few centuries on the roof and all of the radioactivity is gone! Wow!
The author needs to provide a reference, but there's a few ways I can think of that a processing stage, and a few centuries would produce something less radioactive than something produced more recently. I think all of them stem from the ore containing a source material that gets separated through the refining process, but the daughter products from the source don't. Here's one scenario:
Ore = Lead + radio-isotope a + radio-isotope B.
radio-isotope A decays to radio-isotope B
radio-isotope A: 4 billion year half-life.
radio-isotope B: 20 year half life, decays to stable isotope C.
during refining, radio isotope A gets nearly completely refined out to parts per trillion. radio isotope B is similar to lead chemically, and remains at 1 parts per million (at time of refining).
200 years go by. (10 half lives of radio isotope B)
radio isotope B is now at 1/2^10 concentration, or about 1 part per trillion. Significantly less than when it was first refined. The added radioactivity from radio-isotope A decaying into B is negligible due to the long half-life of A.
These numbers and process are obviously made up to show how it MIGHT work. It still remains to be seen if it's actually true or not.
Roman ingots to shield particle detector (Score:4, Informative)
http://www.nature.com/news/2010/100415/full/news.2010.186.html [nature.com]
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it was blessed....
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People don't realize that lead is mildly radioactive, and the decay from solders on the connectors or chassis can also cause bit flips. Very old processed lead, such as that used for the roofs of some European cathedrals, has been used to build supercomputers since more of the radioactivity has decayed.
I'm unclear as how this "processing" of the lead has reduced its natural radiaoctivity...
Pb-210 is in the U-238 and Rn-222 decay chains, so lead ore in the ground has a constant source of Pb-210 being generated due to uranium contamination. Likewise, radon gas can seep into the lead ore deposits and provide a fresh influx of Pb-210. Once the lead is smelted and purified, the uranium contanimation is removed and it's not being exposed to radon so the number of Pb-210 atoms in the sample starts decreasing significantly.
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faulty RAM (Score:5, Interesting)
I've been working with some large microarray datasets recently, and so had to double my computer's memory to 8GB.
As I've done for years, I went to Fry's to get some Corsair chips... installed F13 64bit to replace my older 32bit distro... and crash-o-matic began. Mostly from Chrome and Mercurial.
I ran memtester86+ and sure enough, verified my first purchase of faulty memory.
So, I went back to Fry's and exchanged for another pair of Corsair 2GB chips. This time, I ran memtester86+ first thing... ANOTHER bad set, so back it sent to Fry's.
*Third* set of memory was Kingston, and a trip through memtester86+ verified no errors. Yay!
Computer has been stable, too.
With more and more RAM in computers, my next box will have ECC.
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As RAM gets ever-larger, densities get ever-greater, and the energy requirements for corruption get ever-smaller, the amount of error-correction needed is going to increase. That seems obvious. Well, to an extent. There are space-rated chips that use lead-lined casing to make them radiation-resistant. Having the motherboard run cooler will decrease the thermally-generated random noise in the system. If you're using a full-immersion system, the coolant might easily absorb some of the cosmic rays not otherwis
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Did you buy all new RAM, or add to existing? If you added to existing, did you test just the new RAM, or with the existing in there as well?
Lots of RAM has different timings these days, and even when the timing is supposed to be the same, I've seen new RAM cause problems with old RAM to surface (possibly also from temperature changes). I had a system with 2G (2x1G) Corsair RAM, and then I added another 2G (2x1G) of the same model Corsair; the system started crashing. I assumed (as most would) that the pr
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fascinating (Score:5, Insightful)
Its interesting to me because my first instinct would have been to assume something got corrupted and my first step would have been to reboot. If the problem persisted through a reboot then I might have gone down the rabbit hole in similiar
fashion to try and find and fix the root cause.
There are enough sofware bugs, kernel bugs, driver bugs, hardware hiccups due to marginal equipment, power fluctuation, interference, random noise... and i suppose even cosmic radiation that I would rarely think to spend the time to trace a transient problem unless it was reproducible accross reboots, or at least happened on multiple separate occasions.
Too bad many consumer mainboards don't support ECC (Score:2)
Some of the nicer boards will tolerate ECC memory being inserted, but won't actually do any meaningful error correction (like scrubbing) - but a disturbingly large number of consumer boards (BIOS limitation perhaps?) don't actually do ANYTHING with ECC memory, and the really cheap ones won't even boot with it present. I used to have the same mindset of purchasing only ECC RAM for the same reason - but the unfortunate truth is that hardware support for it just isn't there without spending $$$ on a decent boa
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This is one area where AMD is light years ahead of Intel. With Intel, you have to buy a Xeon and a server chipset to have ECC support, which basically is going to run you at least a grand or two just for the CPU and motherboard (at least if you want an i7 based Xeon). AMD on the other hand supports ECC across the board, and you just need a motherboard which supports it, which is most of them (total cost: <$500).
Thanks for the gouging Intel!
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Wrong. A few Dell PE servers have P4s in them, and -require- ECC memory.
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radioactive isotope in the chip (Score:4, Interesting)
Actually, I recall reading that in the early solid state memory days, they had problems with this. I don't remember what the solution was, but I thought it was to make the circuit somewhat resilient to it, as it was impossible to get 100% neutral epoxy, there's always going to be traces of something radioactive.
I think they tested the cosmic ray theory by running the same chip with and without lead shielding, and did not find a significant difference in errors, they then assumed it was impurities in the chips themselves decaying.
Radioactive packaging (Score:3, Interesting)
The worst problem was with ceramic DIP packages -- the really good ones for when you needed reliability (partly because the plastic ones tended to allow moisture to get in, and then condensation on thermal cycling.) The standard ceramic packaging material containe
Old, old story (Score:5, Interesting)
Back in the early 80's, HP published a paper on random bit errors in RAM. They looked at chips from a variety of vendors and determined that the RAM coming out of Japan was the most reliable. That paper caused a lot of US RAM vendors to shutter their doors as there was a sea change in purchasing habits.
A few years later, I ran into John Scully while we were waiting for a flight. I mentioned the paper to him and asked him how Apple could seriously expect to sell a Macintosh specifically aimed at the Scientific community if it didn't have ECC. He blithely said "it's not a problem..." 20+ years hence and most of us still don't have ECC so it seems he was right.
Re:Old, old story (Score:5, Informative)
For a more recent analysis (by folks at Google and U.Toronto) see "DRAM Errors in the Wild: A Large-Scale Field Study" in ACM SIGMETRICS/Performance 09.
They did an extensive analysis of DRAM failures from many vendors and debunk several myths as well as indicating that the soft error rate can be much higher than previously thought.
Well worth a read...
http://www.cs.toronto.edu/~bianca/papers/sigmetrics09.pdf
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as well as indicating that the soft error rate can be much higher than previously thought.
I'm not sure it really does; true they had enormous average (mean) error rates, but it sounded like this was misleading due to an incredibly skewed distribution. Going by the number of servers with zero errors, one error, and multiple errors over a year, and the failures-vs-age data, I came to the conclusion that there's about a 1/5 chance that you'll see one random single-bit error over a typical lifetime (I think I used 5-6 years), but also a similar chance that part of your ram will go bad after a couple
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*The quad core iMacs have Desktop CPUs in th
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Except for the Mac Book "Pro", that is :)
Cosmic Ray Protection... (Score:2, Funny)
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Had a MySQL problem once. (Once... ha.) (Score:2, Interesting)
I had a mysql replication server which was reading SQL commands from a binary log on a master server. One day after years of operation I noticed an update failed. I didn't see anything at first by looking at the query, but when I looked closely I noticed the query had a single character changed, and of that character only one bit had changed. It was something like a P becoming a Q and thus giving a syntax error.
True story.
Cosmic Rays Tend to Flip Multiple Bits (Score:2)
Cosmic ray events tend to affect multiple neighboring transistors. For this reason, they tend to affect multiple bits. However, by laying out memory cells so immediate neighbors are from different locations, the ability of single-bit-correction-double-bit-detection (SECDED) methods to detect most events is usually preserved.
The main concern is for structures with no error correction, such as the gates in the processor pipeline. Several research ideas have been put forward. See here (PDF) [umich.edu] for a good over
TFA (Score:2)
Reboot? (Score:2)
The article author has obviously never used windows. SOP would be a reboot, which would have solved the problem.
The whole thing would have taken minutes.
Ksplice ... go figure (Score:5, Interesting)
The guy that posted this is a Ksplice developer. In case you didn't knew, KSplice allows you to patch your running kernel without rebooting. Nice.
Anyway, this guys sees a random memory error. He conveniently goes on a debugging rampage, while we all know the most logical first step would be rebooting that damn machine. Random memory errors do happen.
He says he "hasn't gotten around" to memtesting his RAM yet. So, let me get this straight ... he implies that random cosmic rays caused the error, but he hasn't yet tested his ram for what is the most possible cause of the issue?
Then he goes on to explain that you don't even need to reboot your machine due to damn cosmic radiation. Or kernel updates. Because you have Ksplice.
Come on.
I've seen this (Score:3, Informative)
A few years ago I came across a thread on a FreeBSD mailing list where a build of some package was failing and the submitter couldn't tell why because he wasn't a developer. The failure was unusual and no one else could reproduce it. Eventually, the problem was traced back to a character in the source differing from the original. The character was a one-bit difference from the correct character, and it was suggested to the submitter that he reboot and memtest his memory. Sure enough, one single bad bit out of around 512MB.
ha! (Score:5, Insightful)
The really impressive thing is that this guy resisted the urge to just reboot his machine. Otherwise, the clues would have vanished and the expr binary would have run again without any issue.
Maybe that's why the first step one takes when something behaves weird on a Windows system is to reboot it...
Re: (Score:2, Informative)
Same thing just happened to Voyager 2 (Score:2)
http://www.jpl.nasa.gov/news/news.cfm?release=2010-151 [nasa.gov]
Mission managers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., had been operating the spacecraft in engineering mode since May 6. They took this action as they traced the source of the pattern shift to the flip of a single bit in the flight data system computer that packages data to transmit back to Earth.
enterprise hardware/software (Score:2)
I sure am glad my OS and hardware can detect and correct memory errors on the fly and disable the dimms if need be. I know this is a linux-fest, but Solaris fault management is pretty awesome. I've seen it detect a failing cpu, evacuate the memory attached to it and disable the cpu without a hiccup.
Memory Refresh Timing more likely (Score:3, Informative)
I know, cosmic rays sound so much cooler, but it's far more likely he has some crappy memory and/or his memory refresh timings are too high.
DRAM memory cells have to be refreshed pretty often (anywhere from 7.8usec-12usec), otherwise they become unreliable. If his BIOS has the memory timings set to something obscurely long, it may be there are specific rows/cells on his DRAM modules that are too weak to read after bleeding off a bit of charge. Changing the refresh timing would likely improve the situation, causing the memory to refresh it's state more often.
Re:erm.... (Score:4, Informative)
Would it really be so hard to read the article before posting?
Re: (Score:2)
I did read it. I liked the article, actually.
I didn't take into account that he probably never reboots, thereby always using the cached copy.
The k-splice ad on TFA made me laugh in this case.
guess we should put echo 3 > /proc/sys/vm/drop_caches in chrontab.
Re: (Score:2)
I was ready to send him a link to purchase a tinfoil hat (and tinfoil server cover too), but in his article, he says it could be cosmic radiation, or flaky hardware. I'd lay money on the second, and not the first.
I used to joke that cosmic radiation made particular servers crash. We couldn't find any other reason for it, even with a fresh OS (that was identical to our other servers), and swapping various parts. Ya, cosmic radiation went through the building above us, to the
Re: (Score:3, Funny)
I am both shocked and amazed that you eventually broke up.
Re: (Score:2)
Well fear not, it's been a series of upgrades since then. :) My girlfriend now is perfect, I can't imagine a better upgrade from here.
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Re: (Score:3, Funny)
My RAM is shielded against cosmic rays by my mothers basement.
Re: (Score:3, Funny)
You live below your mother's basement???
Sure. In his mother's sub-basement.
Re: (Score:3, Informative)
And no doubt in these super high transistor count and clock frequency CPUs and chips we are using these days there must be devices and methods used inside them to keep the logic transfer and computation validity on the straight and narrow.
Other than ECC on the cache arrays... No. Not a scrap.
If you want reliability on every internal signal and register against cosmic ray strikes, because you're a military or aerospace contractor, you pay boku bucks for it, settle for having way less than what we would cur
Re: (Score:3, Funny)
Walla!
Re: (Score:3, Funny)
Uh, no, not at all... *shifty eyes*
Re: (Score:2)
About a third of all machines in the fleet experience at least one memory error per year, and the average number of correctable errors per year is over 22,000," the report states.
But also 93% of those with errors, have multiple errors. This permits a bit of number crunching [reddit.com], to conclude that 3% have single random errors in a year and 30% probably have bad ram or other hardware issues.
Re: (Score:2)
It should also be noted that this kills performance
By something like 1-5% if I remember correctly, which only matters in benchmarks and dicksize contests.
and may also require read-modify-writes
Um, yeah... that's only possible if you haven't and don't read anything on that same cache line, and even then mightn't happen based on what assumptions your cache makes or might be no different than non-ECC is your cache is only able to talk to your memory in units of a full cache line anyway.