7 ms·

Imaging a Hard Drive with Non-ECC Memory – What Could Go Wrong?

169 points by robertelder 4y ago

mnw21cam 4y ago
Two things. Firstly, I don't think any conclusions can be made about whether dd or dd-rescue is more susceptible to bit flips. It could be that both allocated a buffer, and dd-rescue just happened to be handed the area of memory with the fault in it, which it reused multiple times, where when dd was run that area of memory was used by something else. Memory mapping and usage in a real operating system is highly non-deterministic due to the sheer amount of things that affect it. Secondly, once a good list of known faulty memory addresses had been created by memtest, one can tell the operating system not to use them. Then you can keep using your old hardware without the reliability problems. Although, it is possible that further areas of memory will subsequently fail, and without ECC, you'll still be vulnerable to random (cosmic ray-induced) bit flips.
1letterunixname 4y ago
This wasn't run with a large enough sample size to be statistically valid.
T3OU-736 4y ago
https://youtu.be/aPd8MaCyw5E https://youtu.be/aPd8MaCyw5E ("ShmooCon 2014: You Don' Have The Evidence - Forensic Imaging Tools") was quite an eye-opening talk about common tools, like the article-mentioned `dd` (and its cousin `ddrescue`) and how they deal with I/O errors. To be clear, I do not believe that the tools are at fault - rather, the SATA/SAS/IDE controllers have a different design goal, and software tools can only do so much. Tools like DeepSpar (HW+SW), PC-3000 (also HW+SW) allow for a scary level of nitty-gritty access to HW, including flashing SSD/HDD controller FW in case in went pear-shaped), but for data recovery - be it in a forensic context, or in a context of retrieving important irreplaceable data, I have always had a nerd-lust for those tools. Used them at a previous job, but can't ever justify the price for personal and very infrequent use. :)
hayst4ck 4y ago
Bit flips are totally real, at scale you will definitely see them on large queries. There was a fun talk at DEFCON on bitsquatting, the process of buying 1 bit off domain names and then accepting all incoming connections. Attacks like rowhammer similarly abuse erroneous bit flips. Supposedly microsoft can detect solar activity based on the number of windows crash logs they receive. DEFCON Talk: https://www.youtube.com/watch?v=aT7mnSstKGs https://www.youtube.com/watch?v=aT7mnSstKGs https://en.wikipedia.org/wiki/Bitsquatting https://en.wikipedia.org/wiki/Bitsquatting https://en.wikipedia.org/wiki/Row_hammer https://en.wikipedia.org/wiki/Row_hammer
- 1letterunixname 4y ago
  "Supposedly" is false. The sun doesn't produce cosmic ray-power particles and soft errors aren't affected by sunspot activity. It is affected by altitude and space weather, but not solar activity. https://en.wikipedia.org/wiki/Soft_error https://en.wikipedia.org/wiki/Soft_error I was in the audience of the talk. All devices should be required to use ECC because it's a security risk. Not as much as http:// http:// era, but silent corruption across networks and systems is a thing.
  - colechristensen 4y ago
    > space weather, but not solar activity Space weather is solar activity.
    - dtgriscom 4y ago
      Well, mostly...
    - 1letterunixname 4y ago
      Not entirely. Extrasolar activity is the most likely cause for energetic cosmic rays at the Earth's surface.
  - davidcuddeback 4y ago
    The link you provided contradicts your comment. From the link in your comment: "The average rate of cosmic-ray soft errors is inversely proportional to sunspot activity. That is, the average number of cosmic-ray soft errors decreases during the active portion of the sunspot cycle and increases during the quiet portion."
rrdharan 4y ago
> To even detect this, I needed the patience and discipline to verify the checksum on a 500GB file! Imagine how much more time I could have wasted if I didn't bother to verify the checksum and made use of an important business document that contained one of the 14 bit flips? Unpopular-opinion counterpoint - the odds of this actually happening are vanishingly unlikely. Many file formats have built-in integrity checks and tons of redundancies and waste. I wouldn't want to risk handling extremely valuable private keys or conducting high value cryptocurrency transactions or something, I suppose, on a machine without ECC memory, but that just doesn't really come up in most knowledge worker or end consumer scenarios. The odds of actually getting bit by this in a way that matters to you are really low, which is why nobody cares.
johnklos 4y ago
ECC is good, and I genuinely wish it were more common. Thankfully, Ryzen CPUs support ECC by default (except for pre-7000 series with integrated graphics that aren't "Pro" versions), so long as the motherboard does, too (like all ASRock that I've seen). I'm running several Ryzen servers with ECC. On the other hand, there are many, many systems out there that don't have ECC, nor do they have the option to have ECC. While every video on Youtube wants us to believe that the difference between 580 and 585 frames per second in some silly game or another makes all the difference in the world, for me the difference between a system that runs 10% slower and one that crashes in the middle of the night is actually significant. I test all my systems at a certain memory frequency, then back off to the next slower frequency just to be sure. That doesn't stop memory errors from happening, but most systems have lived their entire lives without having random crashes or random segfaulting. I consider that worthwhile.
- cassianoleal 4y ago
  > so long as the motherboard does, too (like all ASRock that I've seen). I built a home server last year with an ASRock X570M Pro4 [0] with a Ryzen 4750 PRO (which I had to source OEM from Aliexpress as it's not sold direct). I'm not sure what's the current situation, but the only RAM I could find for it was the Kingston Server Premier KSM32ED8 [1], and the ECC premium was not fun to pay. [0] https://www.asrock.com/MB/AMD/X570M%20Pro4/index.asp https://www.asrock.com/MB/AMD/X570M%20Pro4/index.asp [1] https://www.kingston.com/en/memory/server-premier/ddr4-3200mts-ecc-unbuffered-dimm https://www.kingston.com/en/memory/server-premier/ddr4-3200m...
- xwdv 4y ago
  I think you overstate the problem here. Chances are, unless you’ve addressed other more pertinent issues, simply using ECC memory isn’t going to stop systems from crashing in the middle of the night.
  - iopq 4y ago
    I've had random crashes before that were one-off. Like my desktop just froze, and then it never happened again. It only makes sense if it was a random bit-flip. The actual RAM speed never mattered, you can't tell the difference with 150 FPS and 165 FPS (even though my screen's refresh rate is 280Hz)
latchkey 4y ago
I ran a cluster of ~30k blade based computers booting entirely off iPXE. They didn't have any onboard ssd/disk storage or ECC memory. Every day, a few of them would randomly lock up, they'd reboot with a fresh network image and keep on humming.
- jwiz 4y ago
  How do you even get that many computers without ECC? I think all the blades I've seen have ECC as baseline spec.
  - latchkey 4y ago
    They were purpose built and didn't require 100% uptime.
  - undersuit 4y ago
    Google started with "standard PCs", though I'm not finding any info if they used ECC memory. https://blog.codinghorror.com/building-a-computer-the-google-way/ https://blog.codinghorror.com/building-a-computer-the-google... https://patents.google.com/patent/US6549988 https://patents.google.com/patent/US6549988
- yjftsjthsd-h 4y ago
  > Every day, a few of them would randomly lock up, they'd reboot with a fresh network image and keep on humming. There same ones, or random new machines every time?
  - latchkey 4y ago
    Totally random.
    - throwawaylinux 4y ago
      Could easily be software or some other marginal hardware bug though.
moremetadata 4y ago
Moral of the story? Upgrade to DDR5 ram the latest standard which has on-die ECC memory but is not as good at spotting bit flips unlike proper ECC memory with a separate extra data correction chip. https://en.wikipedia.org/wiki/DDR5_SDRAM#:~:text=Unlike%20DDR4%2C%20all%20DDR5%20chips,sending%20data%20to%20the%20CPU https://en.wikipedia.org/wiki/DDR5_SDRAM#:~:text=Unlike%20DD.... Whilst Proper ECC ram chips and motherboards exist, I'm surprised that a cheaper but equally as good as Proper ECC solution doesn't exist although I know some would argue that DDR5 is a step in the right direction of a marathon. I guess the markets know best and chase the numbers, assuming they are also using Proper ECC memory, binary coded decimal and not floating point arithmetic which introduces errors, something central banks have been using for decades? https://en.wikipedia.org/wiki/Floating-point_error_mitigation https://en.wikipedia.org/wiki/Floating-point_error_mitigatio...
- BearOso 4y ago
  DDR5 has enough ECC on chip to make errors effectively impossible. It doesn't provide error data to the CPU, though, so errors in transit can still occur. This is really unlikely, though, and anything not mission-critical will no longer need the extra ECC computation on the CPU-side. (DDR5 encapsulates the memory controller).
  - moremetadata 4y ago
    > This is really unlikely, though, I think you can say that because people are not routinely monitoring their surroundings for ionizing radiation. If this were to change, I think we can start to identify some of those military locations which could be interfering with equipment, that would then expose the weakness of DDR5.
  - ilyt 4y ago
    source on that ? Did anyone tested that ? > This is really unlikely, though, and anything not mission-critical will no longer need the extra ECC computation on the CPU-side. ECC computation is done in hardware anyway
    - 4y ago
ta988 4y ago
I've had a lot of really strange bugs and data loss with my current build (Ryzen with Gskill memory). After running a memtest for 24h i finally saw that two of the four ram sticks were faulty (two bit flips on each only rarely and on a specific test). The company changed them but now a year later without any issues I have another one that failed in exactly the same way. This is the last time I build a non-ECC system for myself.
- muro 4y ago
  Heard a similar story from a friend last week - a faulty RAM stick as well. I'm glad I bought a Threadripper with ECC instead (worth waiting for a Lenovo sale and buy RAM separately)
- mtlmtlmtlmtl 4y ago
  You might want to take a look at your PSU. That seems like a suspicious amount of RAM failure to me. How old is it and what model, if you don't mind me asking? PSU is something I never cheap out on. Always pays for itself in the end. A bad PSU can kill your whole system.
  - ta988 4y ago
    5 years. and the current ram sticks (the 3 that work) can sustain a 3 day memtest with 0 errors (at 3600). They were all able to handle that when I received them back from warranty.
    - mtlmtlmtlmtl 4y ago
      5 years could be getting up there if it's a mid range to low end PSU in terms of reliability. You might want to see if you find your PSU in this list: https://cultists.network/140/psu-tier-list/ https://cultists.network/140/psu-tier-list/
- undersuit 4y ago
  My motherboard isn't rated for more than DDR4-3200 with my old cpu, a Ryzen 7 2700. I could set my memory's XMP profile up and run at DDR4-3466 and memtest would be stable for more than 24 hours but would error before 48. I backed off, DDR-3400, DDR4-3333, DDR4-3266... finally stable in memtest for 96 hours, boot into Windows and run Prime95 Blend workload, 3266 crashes in hours. I finally find a little note in my motherboard manual that older CPUs are limited to DDR4-3200. Set that speed, rock solid, I was even able to tighten the JEDEC timings with guidance from the second XMP profile for DDR4-3133. Gigabyte really did mean DDR4-3200 was the limit for Pinnacle Ridge and older AMD cpus.
tasty_freeze 4y ago
A bit over 20 years ago I had a PC with a memory stick that had gone bad, but not bad enough that it was crashing all the time ... it crashed often enough running windows 98 apps that I attributed all crashes to software nonsense. Back then it was recommended to run a defragger every so often, so I set up a cron job to run it every Saturday night or something like that. The net result was that every file block that got moved made a trip through memory with some small probability of getting corrupted. Often the errors were in files that weren't used that often so I didn't immediately notice. The net result is that after many months of this, I started noticing PDF files that were corrupted, or mp3 files that would hiccup in the middle even though it used to play perfectly before. Sadly, I had ripped my 500-ish CD collection and then had gotten rid of the physical CDs.
muro 4y ago
AFAICT, no current Mac comes with ECC - do they have the same issues? If so, one doesn't hear about them too often.
- jchw 4y ago
  Well, the reason why ECC mattered here is because the RAM was bad, but modern Mac computers do not come with user-serviceable RAM at all, so if you have a problem like this, it's a support ticket anyways, and I'm not even sure there's a true equivalent to Memtest86 for modern Mac computers in the first place. So basically, if it was a RAM problem, there's no point in diagnosing it even if you could; just send your Mac in when you start having issues that seem to be bad RAM. Even with ECC, it's incredibly hard to know that a given one-off issue isn't a memory error, because even ECC can't detect 100% of memory issues. But without ECC, it's also nearly impossible to know if something is a memory error. If it's bad RAM, the same address will likely continue to exhibit bad behavior, but if it's a solar flare, you're never going to know the difference; you will just get incorrect behavior that may or may not crash, and it will be completely impossible to reproduce. One big reason you don't hear it as much is there are not nearly as many data centers filled with Macs. There are definitely a few, and I bet if you got an experience report from them, they could give some idea of how visible memory errors are on Macs (although it's hard, because again, if you don't have ECC, there's not really a good way to know if something is a memory error; you can only really postulate.)
  - AnthonyMouse 4y ago
    ECC is error correcting. A bit gets flipped and it not only detects it but fixes it. Two bits get flipped and it can at least detect it and panic the machine immediately instead of corrupting your data. Without it the corruption is silent. Then this kind of thing happens: https://news.ycombinator.com/item?id=35026440 https://news.ycombinator.com/item?id=35026440 Which is another reason not to solder the storage either. Suppose you have a system board with bad soldered memory and you want to copy your data off of it onto the new one. Well, the memory is flipping random bits as it's copying, but the flash chips are permanently attached to the same board as the bad memory. Otherwise it would have been just a support ticket; now it's something worse.
mtlmtlmtlmtl 4y ago
Amazing technical write up. But if there's no cause for alarm based on SMART, I would just do the memtest right then because that's always my goto for weird undiagnosed problems. I find it's usually not the problem, although when it has been I've ended up wasting a silly amount of time on it(just like this case!). And if there was cause for alarm, I would think long and hard about imaging from the original computer at all. With certain failure modes in drives, just reading could cause more corruption; each failed attempt could lose data. But yeah, happy you did it this way in the end, because I learned a ton from the resulting blog post!
ilyt 4y ago
That reminds me of how I accidentally tracked memory issue to the failing power supply. I noticed (after some windows bluescreen) on memtest that the memory is showing some errors. Ordered another 16GB pair, replaced it and.... the problem persisted. Suspecting something with motherboard I just chalked it to something with mobo and pretty much said "well I'm not replacing mobo now, it will have to wait for next hardware refresh. Gaming PC so no big deal. And now I had 32 GB of RAM in PC. Weirdly enough, problem only happened when running on multi-core memory test. Cue ~1 year after and my power supply just... died. Guessing bad caps I just ordered another and thought nothing of it. On a whim I ran memtest and.... nothing. All fixed. Repeated few times and it was just fine, no bluescreen for ~ 2 years now too. I definitely want to get next machine with ECC but the DDR4 consumer ECC situation looks... weird. I'm not sure whether I should be happy with on-chip ECC, I'd really prefer to have whole CPU-memory pipe ECCed
WirelessGigabit 4y ago
This reminds me of a bug in Google Chrome that was attributed to flipped bit. If anyone has the link, it's missing from my collection...
undersuit 4y ago
>Does increased heat increase the likelihood of memory errors? I think it does. I just got through a round of overclocking my memory. Yes, heat does. >tRFC is the number of cycles for which the DRAM capacitors are "recharged" or refreshed. Because capacitor charge loss is proportional to temperature, RAM operating at higher temperatures may need substantially higher tRFC values. https://github.com/integralfx/MemTestHelper/blob/oc-guide/DDR4%20OC%20Guide.md#temperatures-and-its-effect-on-stability https://github.com/integralfx/MemTestHelper/blob/oc-guide/DD...

169 points by robertelder 4y ago

Two things. Firstly, I don't think any conclusions can be made about whether dd or dd-rescue is more susceptible to bit flips. It could be that both allocated a buffer, and dd-rescue just happened to be handed the area of memory with the fault in it, which it reused multiple times, where when dd was run that area of memory was used by something else. Memory mapping and usage in a real operating system is highly non-deterministic due to the sheer amount of things that affect it. Secondly, once a good list of known faulty memory addresses had been created by memtest, one can tell the operating system not to use them. Then you can keep using your old hardware without the reliability problems. Although, it is possible that further areas of memory will subsequently fail, and without ECC, you'll still be vulnerable to random (cosmic ray-induced) bit flips.

1letterunixname 4y ago

This wasn't run with a large enough sample size to be statistically valid.

T3OU-736 4y ago

https://youtu.be/aPd8MaCyw5E https://youtu.be/aPd8MaCyw5E ("ShmooCon 2014: You Don' Have The Evidence - Forensic Imaging Tools") was quite an eye-opening talk about common tools, like the article-mentioned `dd` (and its cousin `ddrescue`) and how they deal with I/O errors. To be clear, I do not believe that the tools are at fault - rather, the SATA/SAS/IDE controllers have a different design goal, and software tools can only do so much. Tools like DeepSpar (HW+SW), PC-3000 (also HW+SW) allow for a scary level of nitty-gritty access to HW, including flashing SSD/HDD controller FW in case in went pear-shaped), but for data recovery - be it in a forensic context, or in a context of retrieving important irreplaceable data, I have always had a nerd-lust for those tools. Used them at a previous job, but can't ever justify the price for personal and very infrequent use. :)

hayst4ck 4y ago

Bit flips are totally real, at scale you will definitely see them on large queries. There was a fun talk at DEFCON on bitsquatting, the process of buying 1 bit off domain names and then accepting all incoming connections. Attacks like rowhammer similarly abuse erroneous bit flips. Supposedly microsoft can detect solar activity based on the number of windows crash logs they receive. DEFCON Talk: https://www.youtube.com/watch?v=aT7mnSstKGs https://www.youtube.com/watch?v=aT7mnSstKGs https://en.wikipedia.org/wiki/Bitsquatting https://en.wikipedia.org/wiki/Bitsquatting https://en.wikipedia.org/wiki/Row_hammer https://en.wikipedia.org/wiki/Row_hammer

1letterunixname 4y ago
"Supposedly" is false. The sun doesn't produce cosmic ray-power particles and soft errors aren't affected by sunspot activity. It is affected by altitude and space weather, but not solar activity. https://en.wikipedia.org/wiki/Soft_error https://en.wikipedia.org/wiki/Soft_error I was in the audience of the talk. All devices should be required to use ECC because it's a security risk. Not as much as http:// http:// era, but silent corruption across networks and systems is a thing.
- colechristensen 4y ago
  > space weather, but not solar activity Space weather is solar activity.
  - dtgriscom 4y ago
    Well, mostly...
  - 1letterunixname 4y ago
    Not entirely. Extrasolar activity is the most likely cause for energetic cosmic rays at the Earth's surface.
- davidcuddeback 4y ago
  The link you provided contradicts your comment. From the link in your comment: "The average rate of cosmic-ray soft errors is inversely proportional to sunspot activity. That is, the average number of cosmic-ray soft errors decreases during the active portion of the sunspot cycle and increases during the quiet portion."

rrdharan 4y ago

> To even detect this, I needed the patience and discipline to verify the checksum on a 500GB file! Imagine how much more time I could have wasted if I didn't bother to verify the checksum and made use of an important business document that contained one of the 14 bit flips? Unpopular-opinion counterpoint - the odds of this actually happening are vanishingly unlikely. Many file formats have built-in integrity checks and tons of redundancies and waste. I wouldn't want to risk handling extremely valuable private keys or conducting high value cryptocurrency transactions or something, I suppose, on a machine without ECC memory, but that just doesn't really come up in most knowledge worker or end consumer scenarios. The odds of actually getting bit by this in a way that matters to you are really low, which is why nobody cares.

johnklos 4y ago

ECC is good, and I genuinely wish it were more common. Thankfully, Ryzen CPUs support ECC by default (except for pre-7000 series with integrated graphics that aren't "Pro" versions), so long as the motherboard does, too (like all ASRock that I've seen). I'm running several Ryzen servers with ECC. On the other hand, there are many, many systems out there that don't have ECC, nor do they have the option to have ECC. While every video on Youtube wants us to believe that the difference between 580 and 585 frames per second in some silly game or another makes all the difference in the world, for me the difference between a system that runs 10% slower and one that crashes in the middle of the night is actually significant. I test all my systems at a certain memory frequency, then back off to the next slower frequency just to be sure. That doesn't stop memory errors from happening, but most systems have lived their entire lives without having random crashes or random segfaulting. I consider that worthwhile.

cassianoleal 4y ago
> so long as the motherboard does, too (like all ASRock that I've seen). I built a home server last year with an ASRock X570M Pro4 [0] with a Ryzen 4750 PRO (which I had to source OEM from Aliexpress as it's not sold direct). I'm not sure what's the current situation, but the only RAM I could find for it was the Kingston Server Premier KSM32ED8 [1], and the ECC premium was not fun to pay. [0] https://www.asrock.com/MB/AMD/X570M%20Pro4/index.asp https://www.asrock.com/MB/AMD/X570M%20Pro4/index.asp [1] https://www.kingston.com/en/memory/server-premier/ddr4-3200mts-ecc-unbuffered-dimm https://www.kingston.com/en/memory/server-premier/ddr4-3200m...
xwdv 4y ago
I think you overstate the problem here. Chances are, unless you’ve addressed other more pertinent issues, simply using ECC memory isn’t going to stop systems from crashing in the middle of the night.
- iopq 4y ago
  I've had random crashes before that were one-off. Like my desktop just froze, and then it never happened again. It only makes sense if it was a random bit-flip. The actual RAM speed never mattered, you can't tell the difference with 150 FPS and 165 FPS (even though my screen's refresh rate is 280Hz)

latchkey 4y ago

I ran a cluster of ~30k blade based computers booting entirely off iPXE. They didn't have any onboard ssd/disk storage or ECC memory. Every day, a few of them would randomly lock up, they'd reboot with a fresh network image and keep on humming.

jwiz 4y ago
How do you even get that many computers without ECC? I think all the blades I've seen have ECC as baseline spec.
- latchkey 4y ago
  They were purpose built and didn't require 100% uptime.
- undersuit 4y ago
  Google started with "standard PCs", though I'm not finding any info if they used ECC memory. https://blog.codinghorror.com/building-a-computer-the-google-way/ https://blog.codinghorror.com/building-a-computer-the-google... https://patents.google.com/patent/US6549988 https://patents.google.com/patent/US6549988
yjftsjthsd-h 4y ago
> Every day, a few of them would randomly lock up, they'd reboot with a fresh network image and keep on humming. There same ones, or random new machines every time?
- latchkey 4y ago
  Totally random.
  - throwawaylinux 4y ago
    Could easily be software or some other marginal hardware bug though.

moremetadata 4y ago

Moral of the story? Upgrade to DDR5 ram the latest standard which has on-die ECC memory but is not as good at spotting bit flips unlike proper ECC memory with a separate extra data correction chip. https://en.wikipedia.org/wiki/DDR5_SDRAM#:~:text=Unlike%20DDR4%2C%20all%20DDR5%20chips,sending%20data%20to%20the%20CPU https://en.wikipedia.org/wiki/DDR5_SDRAM#:~:text=Unlike%20DD.... Whilst Proper ECC ram chips and motherboards exist, I'm surprised that a cheaper but equally as good as Proper ECC solution doesn't exist although I know some would argue that DDR5 is a step in the right direction of a marathon. I guess the markets know best and chase the numbers, assuming they are also using Proper ECC memory, binary coded decimal and not floating point arithmetic which introduces errors, something central banks have been using for decades? https://en.wikipedia.org/wiki/Floating-point_error_mitigation https://en.wikipedia.org/wiki/Floating-point_error_mitigatio...

BearOso 4y ago
DDR5 has enough ECC on chip to make errors effectively impossible. It doesn't provide error data to the CPU, though, so errors in transit can still occur. This is really unlikely, though, and anything not mission-critical will no longer need the extra ECC computation on the CPU-side. (DDR5 encapsulates the memory controller).
- moremetadata 4y ago
  > This is really unlikely, though, I think you can say that because people are not routinely monitoring their surroundings for ionizing radiation. If this were to change, I think we can start to identify some of those military locations which could be interfering with equipment, that would then expose the weakness of DDR5.
- ilyt 4y ago
  source on that ? Did anyone tested that ? > This is really unlikely, though, and anything not mission-critical will no longer need the extra ECC computation on the CPU-side. ECC computation is done in hardware anyway
  - 4y ago

ta988 4y ago

I've had a lot of really strange bugs and data loss with my current build (Ryzen with Gskill memory). After running a memtest for 24h i finally saw that two of the four ram sticks were faulty (two bit flips on each only rarely and on a specific test). The company changed them but now a year later without any issues I have another one that failed in exactly the same way. This is the last time I build a non-ECC system for myself.

muro 4y ago
Heard a similar story from a friend last week - a faulty RAM stick as well. I'm glad I bought a Threadripper with ECC instead (worth waiting for a Lenovo sale and buy RAM separately)
mtlmtlmtlmtl 4y ago
You might want to take a look at your PSU. That seems like a suspicious amount of RAM failure to me. How old is it and what model, if you don't mind me asking? PSU is something I never cheap out on. Always pays for itself in the end. A bad PSU can kill your whole system.
- ta988 4y ago
  5 years. and the current ram sticks (the 3 that work) can sustain a 3 day memtest with 0 errors (at 3600). They were all able to handle that when I received them back from warranty.
  - mtlmtlmtlmtl 4y ago
    5 years could be getting up there if it's a mid range to low end PSU in terms of reliability. You might want to see if you find your PSU in this list: https://cultists.network/140/psu-tier-list/ https://cultists.network/140/psu-tier-list/
undersuit 4y ago
My motherboard isn't rated for more than DDR4-3200 with my old cpu, a Ryzen 7 2700. I could set my memory's XMP profile up and run at DDR4-3466 and memtest would be stable for more than 24 hours but would error before 48. I backed off, DDR-3400, DDR4-3333, DDR4-3266... finally stable in memtest for 96 hours, boot into Windows and run Prime95 Blend workload, 3266 crashes in hours. I finally find a little note in my motherboard manual that older CPUs are limited to DDR4-3200. Set that speed, rock solid, I was even able to tighten the JEDEC timings with guidance from the second XMP profile for DDR4-3133. Gigabyte really did mean DDR4-3200 was the limit for Pinnacle Ridge and older AMD cpus.

tasty_freeze 4y ago

A bit over 20 years ago I had a PC with a memory stick that had gone bad, but not bad enough that it was crashing all the time ... it crashed often enough running windows 98 apps that I attributed all crashes to software nonsense. Back then it was recommended to run a defragger every so often, so I set up a cron job to run it every Saturday night or something like that. The net result was that every file block that got moved made a trip through memory with some small probability of getting corrupted. Often the errors were in files that weren't used that often so I didn't immediately notice. The net result is that after many months of this, I started noticing PDF files that were corrupted, or mp3 files that would hiccup in the middle even though it used to play perfectly before. Sadly, I had ripped my 500-ish CD collection and then had gotten rid of the physical CDs.

muro 4y ago

AFAICT, no current Mac comes with ECC - do they have the same issues? If so, one doesn't hear about them too often.

jchw 4y ago
Well, the reason why ECC mattered here is because the RAM was bad, but modern Mac computers do not come with user-serviceable RAM at all, so if you have a problem like this, it's a support ticket anyways, and I'm not even sure there's a true equivalent to Memtest86 for modern Mac computers in the first place. So basically, if it was a RAM problem, there's no point in diagnosing it even if you could; just send your Mac in when you start having issues that seem to be bad RAM. Even with ECC, it's incredibly hard to know that a given one-off issue isn't a memory error, because even ECC can't detect 100% of memory issues. But without ECC, it's also nearly impossible to know if something is a memory error. If it's bad RAM, the same address will likely continue to exhibit bad behavior, but if it's a solar flare, you're never going to know the difference; you will just get incorrect behavior that may or may not crash, and it will be completely impossible to reproduce. One big reason you don't hear it as much is there are not nearly as many data centers filled with Macs. There are definitely a few, and I bet if you got an experience report from them, they could give some idea of how visible memory errors are on Macs (although it's hard, because again, if you don't have ECC, there's not really a good way to know if something is a memory error; you can only really postulate.)
- AnthonyMouse 4y ago
  ECC is error correcting. A bit gets flipped and it not only detects it but fixes it. Two bits get flipped and it can at least detect it and panic the machine immediately instead of corrupting your data. Without it the corruption is silent. Then this kind of thing happens: https://news.ycombinator.com/item?id=35026440 https://news.ycombinator.com/item?id=35026440 Which is another reason not to solder the storage either. Suppose you have a system board with bad soldered memory and you want to copy your data off of it onto the new one. Well, the memory is flipping random bits as it's copying, but the flash chips are permanently attached to the same board as the bad memory. Otherwise it would have been just a support ticket; now it's something worse.

mtlmtlmtlmtl 4y ago

Amazing technical write up. But if there's no cause for alarm based on SMART, I would just do the memtest right then because that's always my goto for weird undiagnosed problems. I find it's usually not the problem, although when it has been I've ended up wasting a silly amount of time on it(just like this case!). And if there was cause for alarm, I would think long and hard about imaging from the original computer at all. With certain failure modes in drives, just reading could cause more corruption; each failed attempt could lose data. But yeah, happy you did it this way in the end, because I learned a ton from the resulting blog post!

ilyt 4y ago

That reminds me of how I accidentally tracked memory issue to the failing power supply. I noticed (after some windows bluescreen) on memtest that the memory is showing some errors. Ordered another 16GB pair, replaced it and.... the problem persisted. Suspecting something with motherboard I just chalked it to something with mobo and pretty much said "well I'm not replacing mobo now, it will have to wait for next hardware refresh. Gaming PC so no big deal. And now I had 32 GB of RAM in PC. Weirdly enough, problem only happened when running on multi-core memory test. Cue ~1 year after and my power supply just... died. Guessing bad caps I just ordered another and thought nothing of it. On a whim I ran memtest and.... nothing. All fixed. Repeated few times and it was just fine, no bluescreen for ~ 2 years now too. I definitely want to get next machine with ECC but the DDR4 consumer ECC situation looks... weird. I'm not sure whether I should be happy with on-chip ECC, I'd really prefer to have whole CPU-memory pipe ECCed

WirelessGigabit 4y ago

This reminds me of a bug in Google Chrome that was attributed to flipped bit. If anyone has the link, it's missing from my collection...

undersuit 4y ago

>Does increased heat increase the likelihood of memory errors? I think it does. I just got through a round of overclocking my memory. Yes, heat does. >tRFC is the number of cycles for which the DRAM capacitors are "recharged" or refreshed. Because capacitor charge loss is proportional to temperature, RAM operating at higher temperatures may need substantially higher tRFC values. https://github.com/integralfx/MemTestHelper/blob/oc-guide/DDR4%20OC%20Guide.md#temperatures-and-its-effect-on-stability https://github.com/integralfx/MemTestHelper/blob/oc-guide/DD...