5 ms·

This sounds like laptops are fine, but iMacs and Minis are effed. Curious, what's the real world risk of full OS level corruption and not just data loss?

by yumraj 5y ago

marcan_42 5y ago
Good question. I just started up a loop doing USB-PD hard reboots on my MBA every 18 seconds (that's about one second into the desktop with autologin on, where it should still be doing stuff in the background). Let's see if it eats itself.
- bestouff 5y ago
  Famous last words
  - marcan_42 5y ago
    This is just a test machine I also sometimes use as a dumb terminal around the house; I'm not going to cry if the OS eats itself :P
    - masklinn 5y ago
      Hopefully the ssd doesn’t either though, bricking it would be hilarious but not ideal.
      - marcan_42 5y ago
        Finding out if a DFU restore can recover a corrupted SSD storage would be an interesting test in and of itself! But to be honest, if I end up really bricking a machine for science, that will be worth it for the information it gives us. Obviously I'm not trying to destroy my hardware, but I'm very grateful that I can afford it if it happens thanks to all the support I'm getting from folks for the project.
- joshspankit 5y ago
  How can we get notified about your results?
CrLf 5y ago
Laptops are fine unless your battery has issues and you get occasional power losses, which seems to be not too uncommon for third-party batteries (which themselves are not too uncommon since Apple will charge you an arm and a leg to replace half your laptop if you have a defective battery).
- marcan_42 5y ago
  Bad batteries generally allow for last-gasp handling, and I've definitely seen the SMC throw a fit on some properties a few seconds before shutdown due to the battery being really dead. Not sure if macOS handles this properly, but I'd hope it does, and if it doesn't they could certainly add the feature. It would be quite an extreme case to have a battery failure be so sudden the voltage doesn't drop slowly enough to invoke this.
  - chrismorgan 5y ago
    A fair fraction of the bad batteries I have seen have not behaved like this. Things like immediate power failure on disconnecting AC power, or claiming to be at 30% and then dying, or denying the existence of the battery altogether (two of these have happened to me personally—one at the ripe age of four months rather than due to age—and three or four to other family members). It’s certainly more common for them to just fade fairly rapidly to zero and die there, but it’s by no means rare for them to spontaneously fall over.
    - marcan_42 5y ago
      We're talking different timescales here. All you need is one second or so to command the NVMe controller to flush, and killing other power consumers in the mean time would buy you more time by reducing load, possibly even giving you several minutes the way batteries work (they tend to fall over under load when defective/dead). What may visually appear as power suddenly failing isn't necessarily so at the scale of voltage threshold interrupts and PMICs. What usually happens is battery internal resistance is too high to sustain a given power load, so once load crosses a threshold the system goes into a spiral of doom increasing current as battery voltage decreases and you end up in a shutdown. That's the "30% and suddenly 0% or a shutdown" scenario. But if you catch it before it's too late, you can just stop consuming power and let the NVMe controller flush.
winter_blue 5y ago
Wait, why are iMacs and Minis affected more? (I read the twitter thread; I'm not seeing why.)
- cerved 5y ago
  not battery powered
- Tarq0n 5y ago
  They're dependent on external power, which can acutely fail.
- Gaelan 5y ago
  Laptops have batteries, so an AC power failure doesn't mean they immediately crash: they just keep running on battery until the battery gets low, at which point the system cleanly hibernates.
coldcode 5y ago
Does anyone here run a desktop Mac without a battery backup device? All of my Macs are either laptops or have a hardware backup device, so unlikely a write would be lost due to power failure (unless backup device failed which could happen).
- wila 5y ago
  Sure.. last power failure was like 4 years ago and the one before that was also measured in multiple years. Back when I still used a UPS down here, it was usually the UPS that died and triggered the power failure. So I stopped investing in a UPS.
  - joshspankit 5y ago
    Where I live the power is quite dirty, so even when power losses are measured in years I invest in line-filtering UPS’ to extend the life of my systems. I even lost a MBP to a light flickering event with 0 power loss. Fried the charging circuit straight through the original power brick.

This sounds like laptops are fine, but iMacs and Minis are effed. Curious, what's the real world risk of full OS level corruption and not just data loss?

by yumraj 5y ago

This sounds like laptops are fine, but iMacs and Minis are effed. Curious, what's the real world risk of full OS level corruption and not just data loss?

marcan_42 5y ago

Good question. I just started up a loop doing USB-PD hard reboots on my MBA every 18 seconds (that's about one second into the desktop with autologin on, where it should still be doing stuff in the background). Let's see if it eats itself.

bestouff 5y ago
Famous last words
- marcan_42 5y ago
  This is just a test machine I also sometimes use as a dumb terminal around the house; I'm not going to cry if the OS eats itself :P
  - masklinn 5y ago
    Hopefully the ssd doesn’t either though, bricking it would be hilarious but not ideal.
    - marcan_42 5y ago
      Finding out if a DFU restore can recover a corrupted SSD storage would be an interesting test in and of itself! But to be honest, if I end up really bricking a machine for science, that will be worth it for the information it gives us. Obviously I'm not trying to destroy my hardware, but I'm very grateful that I can afford it if it happens thanks to all the support I'm getting from folks for the project.
joshspankit 5y ago
How can we get notified about your results?

CrLf 5y ago

Laptops are fine unless your battery has issues and you get occasional power losses, which seems to be not too uncommon for third-party batteries (which themselves are not too uncommon since Apple will charge you an arm and a leg to replace half your laptop if you have a defective battery).

marcan_42 5y ago
Bad batteries generally allow for last-gasp handling, and I've definitely seen the SMC throw a fit on some properties a few seconds before shutdown due to the battery being really dead. Not sure if macOS handles this properly, but I'd hope it does, and if it doesn't they could certainly add the feature. It would be quite an extreme case to have a battery failure be so sudden the voltage doesn't drop slowly enough to invoke this.
- chrismorgan 5y ago
  A fair fraction of the bad batteries I have seen have not behaved like this. Things like immediate power failure on disconnecting AC power, or claiming to be at 30% and then dying, or denying the existence of the battery altogether (two of these have happened to me personally—one at the ripe age of four months rather than due to age—and three or four to other family members). It’s certainly more common for them to just fade fairly rapidly to zero and die there, but it’s by no means rare for them to spontaneously fall over.
  - marcan_42 5y ago
    We're talking different timescales here. All you need is one second or so to command the NVMe controller to flush, and killing other power consumers in the mean time would buy you more time by reducing load, possibly even giving you several minutes the way batteries work (they tend to fall over under load when defective/dead). What may visually appear as power suddenly failing isn't necessarily so at the scale of voltage threshold interrupts and PMICs. What usually happens is battery internal resistance is too high to sustain a given power load, so once load crosses a threshold the system goes into a spiral of doom increasing current as battery voltage decreases and you end up in a shutdown. That's the "30% and suddenly 0% or a shutdown" scenario. But if you catch it before it's too late, you can just stop consuming power and let the NVMe controller flush.

winter_blue 5y ago

Wait, why are iMacs and Minis affected more? (I read the twitter thread; I'm not seeing why.)

cerved 5y ago
not battery powered
Tarq0n 5y ago
They're dependent on external power, which can acutely fail.
Gaelan 5y ago
Laptops have batteries, so an AC power failure doesn't mean they immediately crash: they just keep running on battery until the battery gets low, at which point the system cleanly hibernates.

coldcode 5y ago

Does anyone here run a desktop Mac without a battery backup device? All of my Macs are either laptops or have a hardware backup device, so unlikely a write would be lost due to power failure (unless backup device failed which could happen).

wila 5y ago
Sure.. last power failure was like 4 years ago and the one before that was also measured in multiple years. Back when I still used a UPS down here, it was usually the UPS that died and triggered the power failure. So I stopped investing in a UPS.
- joshspankit 5y ago
  Where I live the power is quite dirty, so even when power losses are measured in years I invest in line-filtering UPS’ to extend the life of my systems. I even lost a MBP to a light flickering event with 0 power loss. Fried the charging circuit straight through the original power brick.