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Everything I Know About SSDs

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Re: Everything I Know About SSDs

#61

Post by ajphdiv »

computator wrote: post #41

> Deleted file recovery on a modern SSD is next to impossible for the end user OK, he’s talking about SSDs, but I want to mention that I’ve easily recovered many large deleted files from SD or micro-SD cards (formatted as FAT32 or exFAT) using Norton Unerase or an equivalent utility. Are the controllers for SSDs that different from the controllers for SD cards? Has anyone tried Norton Unerase or an equivalent program…

For the end user it is difficult. Files can be recovered as long garbage collection hasnt happened yet. SSDs require the space to be empty before new data can be written to it. So often times the deleted space is empty. If files are stored in the recycle bin or trash those can still be easily recovered.

It was once explained to me that writing to a HDD is like painting. Where new data can just be painted over the top of the old discarded data. While writing to an SSD is like writing on a chalk board where the old data has to be removed before you can write over it.

Re: Everything I Know About SSDs

#62

Post by wtallis »

rckoepke wrote: post #50
notacoward wrote: post #2

The part about filesystems is slightly incorrect. > The way the file system handles this is incompatible with the workings of NAND flash. That's true of most conventional filesystems, but log-structured filesystems are much more flash-friendly. That's why there has been a resurgence of interest in them, and also why a typical flash translation layer bears a striking resemblance to a log-structured FS. There are also…

> to an HDD all sectors are the same. Also I believe some humans, and (filesystems?) intentionally stored certain data towards the inside/outside of the HDD because the simple cylinder geometry allowed faster reads in those regions. However, I'm not seeing conclusive proof that modern HDDs show performance variation with respect to radius.

> However, I'm not seeing conclusive proof that modern HDDs show performance variation with respect to radius.

They definitely still do; it's fundamental to drives that run at fixed RPM but maintain high areal density across the entire platter. One of the 1TB drives I have lying around does about 183MB/s at the beginning of the disk, 148MB/s in the middle, and 97MB/s at the end.

Re: Everything I Know About SSDs

#63

Post by toast0 »

cattlemansgold wrote: post #43
24gttghh wrote: post #14

Earlier quoted context omitted.

A very basic nuclear reactor can be explained pretty simply I think. You enrich a bunch of let's say uranium. Pack it together in a rod, and put a bunch of those rods in a pond. Those rods have controlled (ideally) nuclear decay from their being in close proximity to other rods which generates a lot of heat, which is transferred to a separate cooling loop that boils water to make steam which drives an electric turbin…

I guess what I meant is that the overall concepts are understandable. Nuclear fuel gets hot, boils water, drives a turbine. For transmissions, different sized gears allow things to turn at different rates. But as soon as I dive into the details, I get lost. How exactly can you control the nuclear decay? How exactly does do the gears in the transmission move around and combine with eachother to create a specific gear…

> How exactly can you control the nuclear decay?

That's what the control rods are for. The uranium in one fuel rod in isolation decays at whatever natural rate, which would warm water but not boil it, and placing the rods near each other allows for the decay products (high energy particles) to interact with other fuel rods and induce more rapid decay.

The control rods slot in between the fuel rods, and absorb the decay products without inducing further nuclear decay. Usually these are graphite rods.

> How exactly does do the gears in the transmission move around and combine with eachother to create a specific gear ratio?

It really depends on the specific transmission, a manual transmission is using the shift lever movement to move the gears into place. An automatic transmission most likely uses solenoids to move things (a solenoid is basically a coil of wires around a tube with a moveable metal rod inside, when you put current through the wire, the metal rod is pulled into the tube, you attach the larger thing you want to move to the end of the rod (sometimes with a pivot or what not), and use a spring, another solenoid, or gravity, etc to make the reverse movement. A solenoid by itself gives you linear movement, if you need rotational movement, one way to do that is have a pivot on the end of the solenoid rod, then a rod from there to one end of a clamp on a shaft, then when the solenoid pulls in its rod, the shaft will rotate (this is the basic mechanism for pinball flippers).

Re: Everything I Know About SSDs

#64

Post by bitexploder »

Kirby64 wrote: post #39
bitexploder wrote: post #20

Earlier quoted context omitted.

My car doesn't even have a transmission. Seriously though, a long time ago, I tore down a 1990 Mustang Automatic transmission and rebuilt it myself and, even back then, it was an amazing piece of machinery. The planetary gear systems are really cool. I don't think I completely understood it, but it was a lot of fun. It did take me two months, heh.

I assume you have an EV? Even EVs have transmissions (unless it's some weird niche car that's completely direct drive). They're just vastly simpler than modern automatic/manual gearboxes, usually a single gear reduction.

Model 3. Calling it a transmission is technically correct, but it is extremely simple. It is single reduction gear as you suggested: https://cleantechnica.com/2018/10/16/tesla-model-3-motor-gea...

Re: Everything I Know About SSDs

#65

Post by Marsymars »

blattimwind wrote: post #4
Ariez wrote: post #3

I was under the impression that if you do not encrypt an SSD from the first use, then any attempt at overwriting with 0s is futile, as well as any other method to securely delete the files. The files will be easily recovered. This guy seems to say the opposite, in that the files are "simply not there anymore", contrary to everything I've read: who's right here?

In practice all SSDs are always encrypted because they use the encryption to whiten the data written to them. That's why "Secure Erase" takes less than a second on SSDs, it doesn't erase anything but the key.

Yes, but in practice, this encryption isn't competently implemented. Hence why MS stopped supporting hardware-accelerated BitLocker.

https://twitter.com/SwiftOnSecurity/status/11774296582599270...

Re: Everything I Know About SSDs

#66

Post by pkaye »

cattlemansgold wrote: post #8

There are a few technologies that I’ve tried very earnestly to understand, only to find out that it’s basically black magic and there’s no use in trying to understand it. Those things are modern car transmissions, nuclear reactors, and SSDs.

I used to work on SSD firmware for a long time. There is a lot of technology and individuals involved but to be honest I find learning on the present day web development stack more daunting at times!

Re: Everything I Know About SSDs

#67

Post by wtallis »

dr_zoidberg wrote: post #55
24gttghh wrote: post #14

Earlier quoted context omitted.

A very basic nuclear reactor can be explained pretty simply I think. You enrich a bunch of let's say uranium. Pack it together in a rod, and put a bunch of those rods in a pond. Those rods have controlled (ideally) nuclear decay from their being in close proximity to other rods which generates a lot of heat, which is transferred to a separate cooling loop that boils water to make steam which drives an electric turbin…

Ok, I've studied the Flash storage (most SSDs these days) technolgy and can be understood like this: * At the "lowest" level, there's a little cell that it's very much an EEPROM (but better, because newer tech). This little cell can hold 1, 2, 3 or 4 bits, depending on gen/tech. * You group a bunch on those cells together and they form a page. Usually it's 1024 cells a page. * You group a bunch of pages together and…

Your quantities are way off if you're trying to describe the kind of NAND flash that goes into SSDs. Typical page sizes are ~16kB plus room for ECC, so a page is several thousand physical memory cells, not just one thousand. Erase blocks are several MB, so at least a thousand pages per erase block. A single die of NAND typically has just 2 or 4 planes, each of which is at least 16GB.

Re: Everything I Know About SSDs

#68

Post by notacoward »

monocasa wrote: post #57
rckoepke wrote: post #50

Earlier quoted context omitted.

> to an HDD all sectors are the same. Also I believe some humans, and (filesystems?) intentionally stored certain data towards the inside/outside of the HDD because the simple cylinder geometry allowed faster reads in those regions. However, I'm not seeing conclusive proof that modern HDDs show performance variation with respect to radius.

Io schedulers would also understand the geometry and reorder commands to minimize seek distance (and therefore seek time).

I used to do some of that a long time ago, and it was actually kind of fun. There's a whole different set of optimizations to do on flash, both for performance and (more importantly in many use cases) power efficiency, and I think that would be fun too.

Re: Everything I Know About SSDs

#69

Post by toast0 »

computator wrote: post #41

> Deleted file recovery on a modern SSD is next to impossible for the end user OK, he’s talking about SSDs, but I want to mention that I’ve easily recovered many large deleted files from SD or micro-SD cards (formatted as FAT32 or exFAT) using Norton Unerase or an equivalent utility. Are the controllers for SSDs that different from the controllers for SD cards? Has anyone tried Norton Unerase or an equivalent program…

It would likely depend of if the filesystem uses TRIM to notify the SSD of deleted sectors.

If it doesn't, the deleted files should retain their data until the filesystem reuses the sector, as normal. If trim is used, the SSD doesn't have to retain the data, but it doesn't necessarily make it unreadable immediately, there are many implementation strategies for trim.

Re: Everything I Know About SSDs

#70

Post by Bozzz »

computator wrote: post #44
cbdumas wrote: post #30

I love a minimal, text-only website as much as the next crotchety HN reader, but a little bit of CSS goes a very long way in terms of readability. Edit: Upon further inspection I see that this page was designed to be hard to read. Very curious.

If the author is reading this, I’d like to ask him to please run his article through a spell checker. All the effort to write a nice article is spoiled by having dozens of typos and spelling mistakes.

I found some of his grammatical choices to be questionable as well.
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