Why I'm usually unnerved when modern SSDs die on us • Hacker News Board

Re: Why I'm usually unnerved when modern SSDs die on us

#111

Post by russdill » Tue, Dec 11, 2018, 6:35 PM UTC

russdill wrote: post #109

pkaye wrote: post #91

I worked on SSD firmware for quite a long time and here is my perspective. Early flash used to fairly reliable with almost minimal error correction. However with increasing density, smaller processes and multi level cells, it has gone progressively less reliable and slower. Here are some of the things that we need to worry about: https://www.flashmemorysummit.com/English/Collaterals/Procee... To compensate for all th…

This is a bit of a misrepresentation. The only flash that never had ECC was NOR. Some embedded systems had NOR, but I'd be incredibly rare to find a consumer SSD with NOR. When designing a NAND memory product, you aim for some max allowed error rate. You choose the error correction algorithm based on that target. Error rates for NAND products are precisely what the designer intended. Because SSDs are so large and the…

Oh, and as someone noted below, spinning disks have also long had error correction in order to reach some target error rate.

Re: Why I'm usually unnerved when modern SSDs die on us

#112

Post by cm2187 » Tue, Dec 11, 2018, 6:39 PM UTC

SomeHacker44 wrote: post #86

cm2187 wrote: post #36

Earlier quoted context omitted.

I think operating systems should be programmed to wipe out a drive completely once early in the life of every user (around age 20-ish) to burn in their brain the need to back up!

My father had the same concept in getting into a car crash early in my driving life. "Now that you have gotten that out of your system (and I'm glad you're fine), don't ever do it again."

Actually that did happen to me early. Luckily enough no harm done. And a lesson for the rest of my life.

Re: Why I'm usually unnerved when modern SSDs die on us

#113

Post by Matthias247 » Tue, Dec 11, 2018, 6:39 PM UTC

pkaye wrote: post #91

I worked on SSD firmware for quite a long time and here is my perspective. Early flash used to fairly reliable with almost minimal error correction. However with increasing density, smaller processes and multi level cells, it has gone progressively less reliable and slower. Here are some of the things that we need to worry about: https://www.flashmemorysummit.com/English/Collaterals/Procee... To compensate for all th…

> Another problem is that the job while rewarding is not very lucrative. The chance of a multi million dollar payoff for an employee is low. I have a higher chance working on a web connected gadget to become a millionaire. So that means it is really hard to recruit those who are top notch programmers who known how to figure out the algorithms, write the code, debug the hardware. Most new grads these days are interested in python, javascript and machine learning.

That seems unfortunately true for most low-level infrastructure software. I am very good at those things, and have a medium amount of experience of building web software. Yet I can find a lot more jobs on the latter domain, and they probably won't pay worse (most likely even better).

Besides pay the non-rewarding things in this domain are mostly that the high complexity is often not properly understood by management, rewarded or taken into account in planning. Which then leads to suboptimal products that have been delivered under time pressure.

Re: Why I'm usually unnerved when modern SSDs die on us

#114

Post by Misdicorl » Tue, Dec 11, 2018, 6:41 PM UTC

loeg wrote: post #96

Misdicorl wrote: post #92

Earlier quoted context omitted.

This seems implausible at first glance. Even making objects flat at the nanometer scale is quite difficult. When you also introduce movement tolerances (e.g. rotation disk is not perfectly aligned), this seems quite extraordinary. Can you provide some references?

Disk platters rotating at 7200 rpm are both perfectly smooth and perfectly aligned. The read head is something like a jumbo jet flying a handful of feet above the (perfectly smooth) ground. It's really crazy how close these things are, moving very fast. And why accelerometers are a significant feature.[0] > Can you provide some references? Wikipedia claims[1]: > In 2011, the flying height in modern drives was a few n…

The claim was hundreds of picometers, which is an order of magnitude smaller than a few nanometers. Literally nothing can be perfectly flat, nor perfectly aligned.

Re: Why I'm usually unnerved when modern SSDs die on us

#115

Post by blattimwind » Tue, Dec 11, 2018, 6:41 PM UTC

hwillis wrote: post #100

cyphar wrote: post #43

Earlier quoted context omitted.

> skates of magnetic readers flying on a cushion of air above a rapidly rotating disc, with the gap separating a few dozen nanometers, often smaller than the process size in the controller's silicon. Complete aside, the fly-height of a magnetic head is actually fractions of a nanometer (i.e. hundreds of picometers). EDIT: I got this from a talk by Bryan Cantrill[1]. The fly-height is allegedly 0.8 nanometers (800 pic…

I do not believe that. 1. I can't find a source that says less than a few nanometers. 2. 300 picometers is roughly the diameter of a helium diatom. The head cannot possibly float through hydrodynamic means if an air molecule can barely even fit under it.

> The head cannot possibly float through hydrodynamic means if an air molecule can barely even fit under it.

It can. Since siblings liked airplane analogies, here is another one: Consider the head to be an airplane. It has somewhat wing-similar features which provide a lifting force, but the actual read/write head sits below those features (like, say, a landing gear is below wings).

Re: Why I'm usually unnerved when modern SSDs die on us

#116

Post by Misdicorl » Tue, Dec 11, 2018, 6:42 PM UTC

cyphar wrote: post #94

Misdicorl wrote: post #92

Earlier quoted context omitted.

This seems implausible at first glance. Even making objects flat at the nanometer scale is quite difficult. When you also introduce movement tolerances (e.g. rotation disk is not perfectly aligned), this seems quite extraordinary. Can you provide some references?

(Sheepishly) My only reference is a talk by Bryan Cantrill[1] where he states that an exec at a hard-drive manufacturer stated it was ".8 nanometers". I will try to find a better source than that. EDIT: There is a paper from 2016 which did an analysis in the difference in the flying height of the head during different operations, and it was measured in Angstroms[2]. I couldn't find one that actually gives a precise v…

This is pretty awesome! Thanks for the links.

Re: Why I'm usually unnerved when modern SSDs die on us

#117

Post by blattimwind » Tue, Dec 11, 2018, 6:44 PM UTC

Misdicorl wrote: post #114

loeg wrote: post #96

Earlier quoted context omitted.

Disk platters rotating at 7200 rpm are both perfectly smooth and perfectly aligned. The read head is something like a jumbo jet flying a handful of feet above the (perfectly smooth) ground. It's really crazy how close these things are, moving very fast. And why accelerometers are a significant feature.[0] > Can you provide some references? Wikipedia claims[1]: > In 2011, the flying height in modern drives was a few n…

The claim was hundreds of picometers, which is an order of magnitude smaller than a few nanometers. Literally nothing can be perfectly flat, nor perfectly aligned.

It doesn't need to be. The basic idea is that the fly height is self-regulating; if the head goes away from the platter, its "lift" is reduced, so the springiness of the arm forces it back to the platter. If it moves closer to the platter, lift is increased, so it moves away. Similarly the tracks don't have to be perfectly round or concentric, because the lowest-level head control system in the drive actively tracks the head's current disk track on the surface; head movements aren't a "rotate 11.57821° to track 28139123", but rather "track 28139123 is around here somewhere, lets find it".

Re: Why I'm usually unnerved when modern SSDs die on us

#118

Post by yzmtf2008 » Tue, Dec 11, 2018, 6:46 PM UTC

sebazzz wrote: post #50

nneonneo wrote: post #29

A major problem with SSDs seems to be “firmware death” - where the flash chips are physically fine (or mostly fine), but the firmware (or firmware memory) has gotten corrupted due to some programming error, electrical glitch, or cosmic ray. I’ve had scores of older SSDs die after things like power outages and sudden shutdown events. This is super frustrating because the data is physically OK but the controller just i…

I have seen some weird issues with SSDs. I had an OCZ Vertex 2 die on me multiple times, but one thing that stood out most is that after a power cycle or complete system shutdown (note: reboots were just fine) everything I had done last time - install software, update Windows, create files - was gone. The state was reverted to before the time it booted. It was like my computer contained some kind of Reborn chip, exce…

Modern SSDs have incredibly large caches. For example, HP EX920, which is a TLC (triple layer cell) SSD, in its 1TB model contains a whooping 200GB of SLC (single layer cell) cache. It's entirely possible that your changes are simply in cache only, and hasn't been committed to the actual storage.

Re: Why I'm usually unnerved when modern SSDs die on us

#119

Post by nneonneo » Tue, Dec 11, 2018, 6:48 PM UTC

soundwave106 wrote: post #67

mkirklions wrote: post #44

Earlier quoted context omitted.

Does this explain why I often can access my 'dead' SSDs with my Ubuntu install rather than Windows? I havent run into this issue for ~4 years, so I'm not sure if this is a solved problem or I got lucky a few years back.

Several years ago I was able to revive a "dead" SSD simply by updating the firmware to the latest version. I haven't had a dead SSD problem in a while though, so I don't know how common firmware issues are now.

FWIW I switched entirely to using Samsung’s SSDs and haven’t had any issues. They seem to be above average for firmware quality, but I don’t have statistics to back that feeling up.

Sometimes the dead SSDs will respond to a handful of commands anyway, meaning that you can attempt a firmware upgrade or reset. That’s the lucky case. But in the majority of cases I’ve seen, the firmware/controller goes into some hard lockup where it no longer processes SATA commands at all. I wish these things had JTAG ports...

Re: Why I'm usually unnerved when modern SSDs die on us

#120

Post by Misdicorl » Tue, Dec 11, 2018, 6:56 PM UTC

blattimwind wrote: post #117

Misdicorl wrote: post #114

Earlier quoted context omitted.

The claim was hundreds of picometers, which is an order of magnitude smaller than a few nanometers. Literally nothing can be perfectly flat, nor perfectly aligned.

It doesn't need to be. The basic idea is that the fly height is self-regulating; if the head goes away from the platter, its "lift" is reduced, so the springiness of the arm forces it back to the platter. If it moves closer to the platter, lift is increased, so it moves away. Similarly the tracks don't have to be perfectly round or concentric, because the lowest-level head control system in the drive actively tracks…

Yes, I understand how feedback control systems work. The question was whether they really have the fidelity to do it at hundred picometer resolution.

I am dubious because this is a pretty incredible feat. This is the length scale at which atom-atom interactions become important. That implies that the crystal lattice structure of both the read/write head and the underlying platter will affect the dynamics of the system!