10 ms·

Not that spinning HDDs are really any different, but SSDs are a perfect example of an entire computer that you attach to yours, and speak with through one of th

Not that spinning HDDs are really any different, but SSDs are a perfect example of an entire computer that you attach to yours, and speak with through one of the (many) storage-oriented protocols. The device itself is a black box, and complex transformations take place between the physical persistence of the data and the logical structures that are exchanged on the wire. There are many layers of indirection, and many things that can go wrong, from fault with the underlying physical storage, a physical fault in the controller, or a logical (software) condition in the controller that puts it in an unrecoverable state. Spinning platter drives have parts that form a more relatable metaphor to humans' notions of wear and tear: 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. They have arms that can move the head over a particular disc radius, and a motor that spins the entire stack of platters. These mechanical components exhibit wear proportional to their use -- this makes intuitive sense, and is also recorded in the SMART attributes, so drives in old age and of many park cycles can be replaced preemptively before they catastrophically fail. SSDs are missing many of the usual mechanisms that would contribute to physical wear leading to sudden catastrophic failure in advanced age. This means that irrespective of their failure rate vs. HDDs, a higher proportion of their catastrophic failures are the fault of the controller. This is discouraging: essentially, the "storage layer" is now quite reliable, so the fallibility of the human-programmed controller is brought into light.

cyphar 8y ago
> 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 picometers). [1]: https://youtu.be/fE2KDzZaxvE?t=1551 https://youtu.be/fE2KDzZaxvE?t=1551
- DoctorOetker 8y ago
  I didnt know they where that close, isn't that similar distances as an scanning tunneling microscope tip to an object? or even closer? Could you provide a reference to a scientific article stating this?
- Misdicorl 8y ago
  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?
  - cyphar 8y ago
    (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 value of the flying height. There is a 2011 paper which states that some system they were testing allowed for 4-9 nm flying heights[3] which is about half-an-order-of-magnitude larger than the claim -- but that's already 7 years old. [1]: https://youtu.be/fE2KDzZaxvE?t=1551 https://youtu.be/fE2KDzZaxvE?t=1551 [2]: http://iieng.org/images/proceedings_pdf/E0116009.pdf http://iieng.org/images/proceedings_pdf/E0116009.pdf [3]: http://maeresearch.ucsd.edu/callafon/publications/2011/UweIEEETonM.pdf http://maeresearch.ucsd.edu/callafon/publications/2011/UweIE...
    - Misdicorl 8y ago
      This is pretty awesome! Thanks for the links.
  - loeg 8y ago
    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 nanometers. and > The "flying height" is constantly decreasing to enable higher areal density. > At 7,200 RPM, the edge of the platter is traveling at over 120 kilometres per hour (75 mph) So you've got a read head flying at 120 km/h => 33 m/s => 33,000,000,000 nm/s at a height of 3nm or less. Picture that! E.g, a 757 typically cruises at 858 km/h => 238 m/s. So picture your 757 flying at an altitude of 21 nm and that's the metaphor, kinda. The read head is a bit smaller than 1/7 of a 757 jet, obviously. [0]: https://en.wikipedia.org/wiki/Head_crash https://en.wikipedia.org/wiki/Head_crash [1]: https://en.wikipedia.org/wiki/Flying_height https://en.wikipedia.org/wiki/Flying_height
marcosdumay 8y ago
SSD's FLASH has plenty of wear and tear. It just has a different format from what happens to mechanical products. It's more similar to some metal that gets scratched on use, and will rust faster or slower depending on the amount of scratches. What we have is that the software is currently less reliable than the memory. There is no fundamental reason for that, it's just that manufacturers put a huge amount of engineering work on reducing the wear, and not so much on programming practices.
AnIdiotOnTheNet 8y ago
> but SSDs are a perfect example of an entire computer that you attach to yours, and speak with through one of the (many) storage-oriented protocols. These days most of what we call a computer could be described this way. Even your compiled machine language is ultimately far more abstracted from what the processor actually does than it was on, say, a 6502.
- zokier 8y ago
  > Even your compiled machine language is ultimately far more abstracted from what the processor actually does than it was on, say, a 6502 Funny that you bring up 6502; that reminds me of 1541 disk drive for C64, which had mostly same 6502 as the host computer (albeit running at slower speed).
  - rmu09 8y ago
    The 6502 in the 1541 runs at 1MHz, that is indeed a bit slower than the NTSC version C64 CPU (1.023MHz), but a bit faster than the PAL version CPU (0.985MHz)
  - AnIdiotOnTheNet 8y ago
    Most disk drives of the time were like that. One of the reasons the Apple II disk drive was so affordable is that Woz just used the Apple II's own 6502 to handle the grunt work, with their disk drive being little more than a drive mechanism, a PROM, and some ICs. Since this is The Woz we're talking about, he went ahead and broke with conventional encoding while he was at it and instead implemented a scheme which allowed for a few extra sectors per track. It might be an interesting exercise to see how many peripherals are connected to your PC right now that have much more computing power than an 1Mhz 6502.
    - ratboy666 8y ago
      The Apple ][ disk encoding was not done to allow "for a few extra sectors per track". Since the Apple ][ did not have a disk controller, the encoding from magnetic flux to bits was handled in software. A 1Mhz 6502 cannot handle the "standard" encoding (things like M2FM) in software as the disc was rotating. Woz's encoding allowed the encoding.
loeg 8y ago
I don't really agree with most of this comment. HDDs are also inscrutable black boxes; many of their failures are controller, rather than media losses; and SSDs also report SMART attributes that are predictive of failure. It's certainly possible HDD vendors have done a more successful job of convincing buyers that failures are attributable to the media rather than the controller, but utilizing the media fully with shingled recording and HAMR and all that jazz really requires a similar degree of controller complexity as an SSD FTL controller.
blattimwind 8y ago
> These mechanical components exhibit wear proportional to their use Actually the spindle isn't touching anything any more, because the spindle/rotor (one part) is supported by a fluid bearing; it basically floats on a thin layer of oil. If the spindle touches the bearing at, essentially any speed that isn't zero, the bearing surfaces are damaged instantly and the resulting burrs and debris will degrade and lock up the bearing very quickly. I believe the only rolling-element/contact bearing used in modern disks is the pivot bearing of the arm assembly.
daemin 8y ago
This reminds me of a story that a lecturer told us at University. That at one point they distributed computations to the drive controllers of the connected (fridge sized) disk drives because they could do so much processing while waiting for the platters to spin into place. So the whole story of a disk being a computer has been true for a long time.
mcv 8y ago
Even so, if SSDs are an entire computer on their own, could that computer at least have the decency to provide some helpful logging?

cyphar 8y ago

> 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 picometers). [1]: https://youtu.be/fE2KDzZaxvE?t=1551 https://youtu.be/fE2KDzZaxvE?t=1551

DoctorOetker 8y ago
I didnt know they where that close, isn't that similar distances as an scanning tunneling microscope tip to an object? or even closer? Could you provide a reference to a scientific article stating this?
Misdicorl 8y ago
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?
- cyphar 8y ago
  (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 value of the flying height. There is a 2011 paper which states that some system they were testing allowed for 4-9 nm flying heights[3] which is about half-an-order-of-magnitude larger than the claim -- but that's already 7 years old. [1]: https://youtu.be/fE2KDzZaxvE?t=1551 https://youtu.be/fE2KDzZaxvE?t=1551 [2]: http://iieng.org/images/proceedings_pdf/E0116009.pdf http://iieng.org/images/proceedings_pdf/E0116009.pdf [3]: http://maeresearch.ucsd.edu/callafon/publications/2011/UweIEEETonM.pdf http://maeresearch.ucsd.edu/callafon/publications/2011/UweIE...
  - Misdicorl 8y ago
    This is pretty awesome! Thanks for the links.
- loeg 8y ago
  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 nanometers. and > The "flying height" is constantly decreasing to enable higher areal density. > At 7,200 RPM, the edge of the platter is traveling at over 120 kilometres per hour (75 mph) So you've got a read head flying at 120 km/h => 33 m/s => 33,000,000,000 nm/s at a height of 3nm or less. Picture that! E.g, a 757 typically cruises at 858 km/h => 238 m/s. So picture your 757 flying at an altitude of 21 nm and that's the metaphor, kinda. The read head is a bit smaller than 1/7 of a 757 jet, obviously. [0]: https://en.wikipedia.org/wiki/Head_crash https://en.wikipedia.org/wiki/Head_crash [1]: https://en.wikipedia.org/wiki/Flying_height https://en.wikipedia.org/wiki/Flying_height

marcosdumay 8y ago

SSD's FLASH has plenty of wear and tear. It just has a different format from what happens to mechanical products. It's more similar to some metal that gets scratched on use, and will rust faster or slower depending on the amount of scratches. What we have is that the software is currently less reliable than the memory. There is no fundamental reason for that, it's just that manufacturers put a huge amount of engineering work on reducing the wear, and not so much on programming practices.

AnIdiotOnTheNet 8y ago

> but SSDs are a perfect example of an entire computer that you attach to yours, and speak with through one of the (many) storage-oriented protocols. These days most of what we call a computer could be described this way. Even your compiled machine language is ultimately far more abstracted from what the processor actually does than it was on, say, a 6502.

zokier 8y ago
> Even your compiled machine language is ultimately far more abstracted from what the processor actually does than it was on, say, a 6502 Funny that you bring up 6502; that reminds me of 1541 disk drive for C64, which had mostly same 6502 as the host computer (albeit running at slower speed).
- rmu09 8y ago
  The 6502 in the 1541 runs at 1MHz, that is indeed a bit slower than the NTSC version C64 CPU (1.023MHz), but a bit faster than the PAL version CPU (0.985MHz)
- AnIdiotOnTheNet 8y ago
  Most disk drives of the time were like that. One of the reasons the Apple II disk drive was so affordable is that Woz just used the Apple II's own 6502 to handle the grunt work, with their disk drive being little more than a drive mechanism, a PROM, and some ICs. Since this is The Woz we're talking about, he went ahead and broke with conventional encoding while he was at it and instead implemented a scheme which allowed for a few extra sectors per track. It might be an interesting exercise to see how many peripherals are connected to your PC right now that have much more computing power than an 1Mhz 6502.
  - ratboy666 8y ago
    The Apple ][ disk encoding was not done to allow "for a few extra sectors per track". Since the Apple ][ did not have a disk controller, the encoding from magnetic flux to bits was handled in software. A 1Mhz 6502 cannot handle the "standard" encoding (things like M2FM) in software as the disc was rotating. Woz's encoding allowed the encoding.

loeg 8y ago

I don't really agree with most of this comment. HDDs are also inscrutable black boxes; many of their failures are controller, rather than media losses; and SSDs also report SMART attributes that are predictive of failure. It's certainly possible HDD vendors have done a more successful job of convincing buyers that failures are attributable to the media rather than the controller, but utilizing the media fully with shingled recording and HAMR and all that jazz really requires a similar degree of controller complexity as an SSD FTL controller.

blattimwind 8y ago

> These mechanical components exhibit wear proportional to their use Actually the spindle isn't touching anything any more, because the spindle/rotor (one part) is supported by a fluid bearing; it basically floats on a thin layer of oil. If the spindle touches the bearing at, essentially any speed that isn't zero, the bearing surfaces are damaged instantly and the resulting burrs and debris will degrade and lock up the bearing very quickly. I believe the only rolling-element/contact bearing used in modern disks is the pivot bearing of the arm assembly.

daemin 8y ago

This reminds me of a story that a lecturer told us at University. That at one point they distributed computations to the drive controllers of the connected (fridge sized) disk drives because they could do so much processing while waiting for the platters to spin into place. So the whole story of a disk being a computer has been true for a long time.

mcv 8y ago

Even so, if SSDs are an entire computer on their own, could that computer at least have the decency to provide some helpful logging?