5 ms·

From 6 inches away? Unless this was a hockey-puck sized magnet I'm calling it a coincidence. > (harvested from an old hard disk drive) Okay, this is making ev

by dpedu 9y ago

From 6 inches away? Unless this was a hockey-puck sized magnet I'm calling it a coincidence. > (harvested from an old hard disk drive) Okay, this is making even less sense. "Hard drive magnets", in a drive, are millimeters from the spinning platters. I refuse to believe that the same magnet, moved 6 inches away from the computer caused catastrophic damage.

quickben 9y ago
But it will mess up the power flow. Misbehaving powesupplies destroy HDDs.
- cptskippy 9y ago
  So a magnet held 6 inches away from the PC did more damage than the one inside the HDD literally inside the PC?
  - 2muchcoffeeman 9y ago
    Yeah, I hope people realise that everybody has these magnets IN their computer. You might have a NAS in which case you have several of these magnets much closer than 6 inches to the other drives and power supply and nothing happens. Magnets near your or even on the computer do nothing.
    - Scramblejams 9y ago
      Magnets induce a current when moved relative to a conductor. The magnets you mention aren’t moving.
      - harshreality 9y ago
        So what you're saying is that nobody can hot swap drives in a NAS without destroying neighboring drives? I don't buy that either.
        quickben 9y ago
        No, what he is saying, is that moving magnetic field, induces current, and can mess up the cheap power supply and/or other components, which can then mess up the drives. In a server, the power supply is on the other end of the chasis. In a laptop, it's a lot closer to the internals. > I don't buy that either. Theory: https://en.wikipedia.org/wiki/Electromagnetic_induction https://en.wikipedia.org/wiki/Electromagnetic_induction The forward model: https://www.youtube.com/watch?v=UL_ryxub-RA https://www.youtube.com/watch?v=UL_ryxub-RA The reverse model: https://www.youtube.com/watch?v=J9b0J29OzAU https://www.youtube.com/watch?v=J9b0J29OzAU The big ones: https://en.wikipedia.org/wiki/List_of_conventional_hydroelectric_power_stations https://en.wikipedia.org/wiki/List_of_conventional_hydroelec... Note: the Three Gorges: 22 GW For comparison, nuclear power: https://www.nei.org/Knowledge-Center/Nuclear-Statistics/US-Nuclear-Power-Plants https://www.nei.org/Knowledge-Center/Nuclear-Statistics/US-N... Largest U.S. nuclear plant: Palo Verde (Arizona) produces around 4 GW. For home applications: http://www.ebay.com/bhp/hydro-electric http://www.ebay.com/bhp/hydro-electric
        ars 9y ago
        Do you understand what you are saying? A person, moving a magnet near a single wire - not even a coil - is going to induce utterly insignificant amounts of electricity. You'd need lab equipment to even detect it. It will do absolutely nothing whatsoever to computer electronics.
        quickben 9y ago
        Open a powesupply before your next reply.
        ars 9y ago
        What am I supposed to reply to? Instead, why don't you take a multimeter and see if you can measure any voltage (never mind current) by moving a magnet, by hand, near a single non-coiled wire.
        9y ago
      - sandworm101 9y ago
        >> moved relative to a conductor Yes. The magnet is stationary and the spinning drive plate is moving the data, the conductor, very rapidly relative to the magnet. (imho the real issue is the large metal box surrounding the drive plates. It's hard to feel a magnet from inside a metal house.)
      - zaarn 9y ago
        When you swap drives, they are. Yet people don't have mysterious data loss when swapping drives out of their bays.
    - deleted 9y ago
      [deleted]
  - deleted 9y ago
    [deleted]
EvanAnderson 9y ago
I will definitely concede that the 6" number may be an incorrect memory. It certainly may have been closer, but it wasn't right on top of the unit. If it was a coincidence it was certainly well-timed. I don't have the Thinkpad anymore, but I do still have some 2.5" PATA drives. It might be interesting to test this and make a video. Here's a picture of the magnet in question (it holds stuff to my refrigerator now), w/ a penny for scale: http://mx02.wellbury.com/misc/20171203-Magnet_of_doom.jpg http://mx02.wellbury.com/misc/20171203-Magnet_of_doom.jpg This magnet was pulled from a Micropolis 9GB SCA-II 3.5" low-profile drive dating from roughly 1998 (I had a crap-ton of these drives and, as they died, I pulled their magnets, so I have a bunch of these). These particular magnets will stick to each other thru my 3" thick butcher block table. They are physically larger (substantially thicker) than the ones I've pulled from newer drives. Edit: I assume that the data and servo tracks written to the drive are done so in the presence of the magnetic flux of the magnets supporting the voice coil. I always just assumed that adding a substantial new source of magnetic flux (the magnet in my hand) either induced a current or magnetized some component in the drive.
- syshum 9y ago
  >> They are physically larger (substantially thicker) than the ones I've pulled from newer drives. Not really, they look very close in size to current Enterprise Drives (https://imgur.com/2HjuuKM https://imgur.com/2HjuuKM), Of course I have removed the Metal backing plate from mine Now consumer drives do have smaller magnets (that is one way to save cost) Here is a photo of the 4 styles of magnets I still personally have, the smaller magnets are either out of consumer drives and 2.5in drives manufactured in the last 7 years https://imgur.com/59XjVPm https://imgur.com/59XjVPm And just for fun a small assortment of my collection because why not https://imgur.com/bW6ycRI https://imgur.com/bW6ycRI
  - EvanAnderson 9y ago
    I've only had the opportunity to tear down a few consumer drives in the last few years. I haven't seen inside an enterprise-class drive in a few years. (I've stopped dealing with hardware directly for my Customers, and I haven't purchased much hardware for personal use over the last few years.) I've found scavenged hard drive magnets to be very useful for odd jobs. One served several years holding up the fallen head-liner over the drivers seat in one of my crappier cars.
Waterluvian 9y ago
I stack hard drives and they keep working.
- EvanAnderson 9y ago
  Absolutely. Hard disk drives don't stick to your refrigerator (like a naked magnet does) either. My layman's guess would be that the fields generated by the magnets in opposition in the voice coil are somehow "balanced", so that the net magnetic field produced by the drive is negligible.
  - SAI_Peregrinus 9y ago
    It's simpler than that. They're held in an iron ring. This confines the field nicely, the permeability of the iron is quite high.
ars 9y ago
I agree that it makes no sense. A magnet outside the case is not going to do anything to the platters. kees99 posted a possible explanation, where the magnet moves the voice coil, which ends up destroying the drive by writing data in the wrong places.
- dpedu 9y ago
  This can't happen either. Early hard drives (and I mean early: the 80s) needed precise head alignment (in respect to the how far the head is from the center of the platter) in order to read or write data in the correct location. If you've heard of "low-level" formatting, that's when a on-platter layout unique to the head and head movement mechanisms of the host drive is created. Modern drives, however, are designed to "follow" the tracks that are cookie-cutter imprinted onto the platters. We use this design now as it's far easier to design a head that reads tracks and makes slight adjustments to stay on track, vs a head that needs to move to an absolute exact position. In other words, modern drives are designed to combat this exact problem.

by dpedu 9y ago

quickben 9y ago

But it will mess up the power flow. Misbehaving powesupplies destroy HDDs.

cptskippy 9y ago
So a magnet held 6 inches away from the PC did more damage than the one inside the HDD literally inside the PC?
- 2muchcoffeeman 9y ago
  Yeah, I hope people realise that everybody has these magnets IN their computer. You might have a NAS in which case you have several of these magnets much closer than 6 inches to the other drives and power supply and nothing happens. Magnets near your or even on the computer do nothing.
  - Scramblejams 9y ago
    Magnets induce a current when moved relative to a conductor. The magnets you mention aren’t moving.
    - harshreality 9y ago
      So what you're saying is that nobody can hot swap drives in a NAS without destroying neighboring drives? I don't buy that either.
      - quickben 9y ago
        No, what he is saying, is that moving magnetic field, induces current, and can mess up the cheap power supply and/or other components, which can then mess up the drives. In a server, the power supply is on the other end of the chasis. In a laptop, it's a lot closer to the internals. > I don't buy that either. Theory: https://en.wikipedia.org/wiki/Electromagnetic_induction https://en.wikipedia.org/wiki/Electromagnetic_induction The forward model: https://www.youtube.com/watch?v=UL_ryxub-RA https://www.youtube.com/watch?v=UL_ryxub-RA The reverse model: https://www.youtube.com/watch?v=J9b0J29OzAU https://www.youtube.com/watch?v=J9b0J29OzAU The big ones: https://en.wikipedia.org/wiki/List_of_conventional_hydroelectric_power_stations https://en.wikipedia.org/wiki/List_of_conventional_hydroelec... Note: the Three Gorges: 22 GW For comparison, nuclear power: https://www.nei.org/Knowledge-Center/Nuclear-Statistics/US-Nuclear-Power-Plants https://www.nei.org/Knowledge-Center/Nuclear-Statistics/US-N... Largest U.S. nuclear plant: Palo Verde (Arizona) produces around 4 GW. For home applications: http://www.ebay.com/bhp/hydro-electric http://www.ebay.com/bhp/hydro-electric
        ars 9y ago
        Do you understand what you are saying? A person, moving a magnet near a single wire - not even a coil - is going to induce utterly insignificant amounts of electricity. You'd need lab equipment to even detect it. It will do absolutely nothing whatsoever to computer electronics.
        quickben 9y ago
        Open a powesupply before your next reply.
        ars 9y ago
        What am I supposed to reply to? Instead, why don't you take a multimeter and see if you can measure any voltage (never mind current) by moving a magnet, by hand, near a single non-coiled wire.
        9y ago
    - sandworm101 9y ago
      >> moved relative to a conductor Yes. The magnet is stationary and the spinning drive plate is moving the data, the conductor, very rapidly relative to the magnet. (imho the real issue is the large metal box surrounding the drive plates. It's hard to feel a magnet from inside a metal house.)
    - zaarn 9y ago
      When you swap drives, they are. Yet people don't have mysterious data loss when swapping drives out of their bays.
  - deleted 9y ago
    [deleted]
- deleted 9y ago
  [deleted]

EvanAnderson 9y ago

I will definitely concede that the 6" number may be an incorrect memory. It certainly may have been closer, but it wasn't right on top of the unit. If it was a coincidence it was certainly well-timed. I don't have the Thinkpad anymore, but I do still have some 2.5" PATA drives. It might be interesting to test this and make a video. Here's a picture of the magnet in question (it holds stuff to my refrigerator now), w/ a penny for scale: http://mx02.wellbury.com/misc/20171203-Magnet_of_doom.jpg http://mx02.wellbury.com/misc/20171203-Magnet_of_doom.jpg This magnet was pulled from a Micropolis 9GB SCA-II 3.5" low-profile drive dating from roughly 1998 (I had a crap-ton of these drives and, as they died, I pulled their magnets, so I have a bunch of these). These particular magnets will stick to each other thru my 3" thick butcher block table. They are physically larger (substantially thicker) than the ones I've pulled from newer drives. Edit: I assume that the data and servo tracks written to the drive are done so in the presence of the magnetic flux of the magnets supporting the voice coil. I always just assumed that adding a substantial new source of magnetic flux (the magnet in my hand) either induced a current or magnetized some component in the drive.

syshum 9y ago
>> They are physically larger (substantially thicker) than the ones I've pulled from newer drives. Not really, they look very close in size to current Enterprise Drives (https://imgur.com/2HjuuKM https://imgur.com/2HjuuKM), Of course I have removed the Metal backing plate from mine Now consumer drives do have smaller magnets (that is one way to save cost) Here is a photo of the 4 styles of magnets I still personally have, the smaller magnets are either out of consumer drives and 2.5in drives manufactured in the last 7 years https://imgur.com/59XjVPm https://imgur.com/59XjVPm And just for fun a small assortment of my collection because why not https://imgur.com/bW6ycRI https://imgur.com/bW6ycRI
- EvanAnderson 9y ago
  I've only had the opportunity to tear down a few consumer drives in the last few years. I haven't seen inside an enterprise-class drive in a few years. (I've stopped dealing with hardware directly for my Customers, and I haven't purchased much hardware for personal use over the last few years.) I've found scavenged hard drive magnets to be very useful for odd jobs. One served several years holding up the fallen head-liner over the drivers seat in one of my crappier cars.

Waterluvian 9y ago

I stack hard drives and they keep working.

EvanAnderson 9y ago
Absolutely. Hard disk drives don't stick to your refrigerator (like a naked magnet does) either. My layman's guess would be that the fields generated by the magnets in opposition in the voice coil are somehow "balanced", so that the net magnetic field produced by the drive is negligible.
- SAI_Peregrinus 9y ago
  It's simpler than that. They're held in an iron ring. This confines the field nicely, the permeability of the iron is quite high.

ars 9y ago

I agree that it makes no sense. A magnet outside the case is not going to do anything to the platters. kees99 posted a possible explanation, where the magnet moves the voice coil, which ends up destroying the drive by writing data in the wrong places.

dpedu 9y ago
This can't happen either. Early hard drives (and I mean early: the 80s) needed precise head alignment (in respect to the how far the head is from the center of the platter) in order to read or write data in the correct location. If you've heard of "low-level" formatting, that's when a on-platter layout unique to the head and head movement mechanisms of the host drive is created. Modern drives, however, are designed to "follow" the tracks that are cookie-cutter imprinted onto the platters. We use this design now as it's far easier to design a head that reads tracks and makes slight adjustments to stay on track, vs a head that needs to move to an absolute exact position. In other words, modern drives are designed to combat this exact problem.