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Comment by dathinab | Hacker News Reader

Probably more like downvoted because missing the point.

Sure fsync allows that behavior, but also it's so widely misunderstood that a lot of programs which should do a "full" flush only do a fsync, including Benchmarks. In which case they are not comparable and doing so is cheating.

But that's not the point!

The point is that with the M1 Macs SSDs the performance with fully flushing to disk is abysmal bad.

And as such any application with cares for data integrity and does a full flush can expect noticable performance degradation.

The fact that Apple neither forces frequent full syncs or at least full syncs when a Application is closed doesn't make it better.

Though it is also not surprising as it's not the first time Apple set things up under the assumption their hardware is unfailable.

And maybe for a desktop focused high end designs where most devices sold are battery powered that is a reasonable design choice.

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"And maybe for a desktop focused high end designs where most devices sold are battery powered that is a reasonable design choice"

Does the battery last forever? Do they never shut down from overheating, shut down from being too cold, freeze up, they are water and coffee proof?

Talk to anyone that repairs mac about how high-end and reliable their designs trully are - they are better than bottomn of the barrel craptops, sure, but not particularly amazing and have some astounding design flaws.

How cold is too cold for a computer?

The CPU can't possibly get too cold. See for example overclocking performed by cooling the CPU with liquid nitrogen. Condensation is a factor as is lost of ductility of plastic at low temp making it brittle. Expansion and contraction of materials especially when different materials expand to different degrees.

"The CPU can't possibly get too cold" - Untrue. There are plenty of chips with what overclockers like to call "cold bugs".

Sequential logic (flipflops) has a setup time requirement. This means the combinatorial computation between any two connected pairs of flops (output of flop A to input of flop B) has to do its job fast enough such that the input of B stops toggling some amount of time before the next clock edge arrives at the flipflop. Violate that timing, and B will sometimes sample the wrong value, leading to an error.

Setup time is what most people are thinking about when they use LN2 or other exotic forms of cooling. By cooling things down, you usually improve the performance of combinatorial logic, which provides more setup time margin, allowing you to increase clock speed until setup time margin is small again.

But flops also have hold time requirements - their inputs have to remain stable for some amount of time after the clock edge, not just before. It's here where we can run into problems if the circuit is too cold. Imagine a path with relatively little combinatorial logic, and not much wire delay. If you make that path too fast, it might start violating hold time on the destination flop. Boom, shit doesn't work.

I've had my phone shut off on me from being out in the Chicago cold for a couple hours. Battery over 50% when I brought it back inside and warmed it up.

If i go ousode in winter, the bsttery dies around zero degrees. Keep in mind that you laptop could be in a bag in sleep mode or idle

The biggest thing is the battery. The CPU doesnt get too cold, but batteries degrade or stop performing when they get too cold.

Edit: For actual temperatures, in my experience its when the device is in use for a sustained amount of time in under 10f weather

Incidentally CPUs do get too cold, not at a reasonable temperature, but sufficiently low temperatures do change the characteristics of semi conductors. Not something to worry about if you're not using liquid nitrogen (or colder).

Many phones, laptops cameras and similar are only guaranteeing functionally by above 0 degree....

Luckily they often operate in lower temperatures too, but not seldomly by hoping they don't get cooled that much themself (because they are e.g. in your pocket).

0 degree what?

Fahrenheit, Celsius, horizontal angle?

As the article points out, a lot of those cases can be detected with advanced notice (dying battery, and overheating - probably even being too cold). In those cases the OS makes sure all the caches are flushed.

Spilled drinks are a viable cause for concern, but if they do enough damage to cause an unexpected shutdown, you've probably got bigger issues than unflushed cache.

I think that's misleading.

On many laptops even with water damage you can recover your local data fully, not do for Macs (for more reasons then just data loss/corruption due to non flushing).

Especially if you are already in a bad situation you don't want your OS to make it worse.

"In those cases the OS makes sure all the caches are flushed."

I have never heard of this functionality being included in any major OS, could you please provide some reference to this being documented?

I mean the Apple hardware in question is usually a laptop, which has its own very well instrumented battery backup. In most cases the hardware knows well in advance if the battery is gonna run dry.

And yes the hardware is failable. But the kind if failure that would cause the device to completely lose power is extremely rare. The OS has many chances to take the hint and flush the cache before powering down.

Note: this is pure conjecture.

> The point is that with the M1 Macs SSDs the performance with fully flushing to disk is abysmal bad.

How sure are we the drives that flush caches more quickly are actually flushing the caches?

Good Point.

A simple test can be to see the degree of dataloss you can occur with a hard power off.

I think the author did that test for M1 Mac but idk. if they did the test with the other laptops.

But then the M1 Mac is slower when flushing then most SSDs out there and even some HDDs. I think if most SSDs wouldn't flush data at all we would know of that and I should have run into problems with the few docent hard resets I ran into in the last few years. (And sure there are probably some SSDs which cheap out on cache flushing in a dangerous way, but most shouldn't as far as I can tell).

We’d see data loss only if the power loss or hard reset happened before the data is actually flushed. After the data is accepted into the buffer there would be a narrow time window when it could occur. Also, a hard reset on the computer side may not be reflected on the storage embedded electronics.

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