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Recover HD Using a Magnet

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Re: Recover HD Using a Magnet

#41
post #14

My anecdote: Around 1993 I had a Commodore Amiga with an A590 external hard drive. A big enclosure that could be connected to the expansion port on the left of an Amiga 500, containing a very precious 20MB hard disk. One day, it stopped working. I tried everything but I couldn’t get it to work. A friend offered to take a look at it so I put it in my backpack and took the train to my friend. When connected to his A500…

"sticktion" was an issue with some early Mac drives.

In 1989, I did an internship with Imprimis, which was later sold to Seagate.

I worked in the Manufacturing Engineering group, and specifically with the Engineers behind the “Wren” line of hard drives. IIRC, up to the Wren V, they had problems with the lubricant sometimes overheating and leaking out of the spindle onto the platters. When the hard drive spun down, the heads would be glued to the media by the lubricant, thus resulting in stiction.

They developed a “thermalwriter“ test process for the drives to put them through heat conditions way beyond what they might experience in the field, and then developed lubricants that could withstand the heat. They were very proud of this process. But there were still lots of old drives out there.

One of the things the clean room would sometimes do is take hard drives from important clients and try to recover them. I saw a lot of nasty failures, many of which were a result of inappropriate techniques being applied to try to temporarily free the heads.

There was a lot of FUD at the time on what would later be called “The Internet”, so one of my first contributions to the community was to take the knowledge of the engineers at the company and developed a FAQ that I posted to the various USENET newsgroups, on the right — and wrong — ways to try to address this issue in the field.

Sometimes I wonder if that FAQ ever survived.

Re: Recover HD Using a Magnet

#42

My story: In 1996 or 97, a friend brought me his Compaq Deskpro, the SCSI HDD had stopped working. No sound at all, dead. Tried everything, checked voltages, reconnected cables trying to clear any oxidation. Wouldn't spin at all. Well, called it a night. Next day, decided to take it out of the chassis for a last test, connected outside. Not only it spun, it worked fine!!! WTH???? Well, into the chassis it went. Nothi…

Perhaps a defect in a cable or connector such as a broken wire or a dry solder joint? These often cause problems that mysteriously appear or disappear as the cable is moved and the changing forces on the defect make and break the connection.

Re: Recover HD Using a Magnet

#43
post #4
post #2

How did the data not get destroyed by the magnet?

There are actually very powerful permanent magnets inside of every spinning hard drive already, so clearly there's more to destroying data than just having a magnet nearby. https://www.kjmagnetics.com/blog.asp?p=hard-drive-destructio... has a writeup about trying and failing to wipe a drive with extremely powerful magnets.

There are degaussing devices that look like microwave ovens, and for all I know, that might be largely how they operate.

But outside of those, no magnet that you can hold in your hand will demagnetize a modern hard drive at any distance outside of the case, because there are magnets inside the case that are stronger than you can hold in your hands, and they’re used to move the head/arm assembly at mind-blowing speeds — and accuracy.

I have some old Imprimis Wren VII hard drive magnets still on my dad’s fridge, from the time when I did an internship there in 1989. I won’t say that you can’t remove them from the fridge, but they are stuck on there extremely well, and there are a number of people who had been injured by having their hand or fingers caught between those magnets and a ferrous metal object — like a fridge.

And that was 1989. The magnets they use now are much stronger.

Now, if you happened to put a hard drive inside an MRI machine, that would do the job. But then you’re also talking about a machine that could suck up a vacuum cleaner from across the room and turn it into a lethal projectile. A proper degausser will be a lot weaker than an MRI machine.

Re: Recover HD Using a Magnet

#44
post #30
post #4

Earlier quoted context omitted.

There are actually very powerful permanent magnets inside of every spinning hard drive already, so clearly there's more to destroying data than just having a magnet nearby. https://www.kjmagnetics.com/blog.asp?p=hard-drive-destructio... has a writeup about trying and failing to wipe a drive with extremely powerful magnets.

You know what is sad about a small business (kjmagnetics.com) that you linked to? They are exactly what will be killed off by Amazon. The small and knowledgeable specialty store very similar as I am sure many of us remembered happened to 'Stereo Stores' once the big boxes stores came along (or hardware stores). Nothing new about this of course just that with Amazon it's greatly accelerated.

Amazon is 8 years older than K&J Magnetics...but sure

Re: Recover HD Using a Magnet

#46
post #14

My anecdote: Around 1993 I had a Commodore Amiga with an A590 external hard drive. A big enclosure that could be connected to the expansion port on the left of an Amiga 500, containing a very precious 20MB hard disk. One day, it stopped working. I tried everything but I couldn’t get it to work. A friend offered to take a look at it so I put it in my backpack and took the train to my friend. When connected to his A500…

FWIW the failure mode (which was also common in drives for the SPARCStation at the time) was called "stiction." That occurred when the drive parked the heads, after power down, into the landing zone on the platter.

At Sun we took apart a number of failed drives (which could also be recovered sometimes by giving them a sharp twist) and hunted for the root cause. The answer was that over some time the drive heads became smoother and the surface of the landing zone also became smoother. When the tiny edges of the head had been removed by this process, the surface of the head was pretty much optically smooth (very little variation) and when it landed in a part of the landing zone that was similarly smooth the surfaces would push out the air between them and become stuck just by air pressure and surface friction (stiction). The drive would not spin up until the head had lifted off the surface. The firmware issue was that head lift off was checked for so quickly that the power up of the spindle was aborted before anything happened (this was to prevent damage to the head by dragging it along the platter's landing zone). By jostling the drive you could manually cause the platters to rotate and if you found a spot that wasn't completely smooth (or if you managed to have the heads move out of the landing zone) the surface would be rough enough that the head wasn't being held down and it could lift off again.

Seagate gave us a firmware fix which basically waited longer for the heads to lift off allowing the spindle motor to move the platter a bit before giving up. Quantum (the other disk supplier) beefed up the retract solenoid and gave us firmware that would try 'regular' retract and then 'heavy' retract before giving up. For a pretty long time I had a Seagate drive that had been disassembled to the point of exposing the heads and platters so that the effect could be demonstrated to skeptical engineers.

Re: Recover HD Using a Magnet

#47

Clever! I'm stuck on a problem right now as well, I'm trying to boot an old server (Supermicro, dual CPU) to verify something and for the life of me I can't figure out what is wrong with it. It doesn't do anything when you power it up, even the power led on the board doesn't light up. Forcing the powersupply to 'on' does light up the LED but the system still won't boot. Already put a fresh 3V cell in it, stripped it…

Oh, did any caps blow? There were some counterfeit ones going around some time ago...

Re: Recover HD Using a Magnet

#48
post #14

My anecdote: Around 1993 I had a Commodore Amiga with an A590 external hard drive. A big enclosure that could be connected to the expansion port on the left of an Amiga 500, containing a very precious 20MB hard disk. One day, it stopped working. I tried everything but I couldn’t get it to work. A friend offered to take a look at it so I put it in my backpack and took the train to my friend. When connected to his A500…

Might as well share mine: one day the magic smoke[0] left a lot of components on my PC, including the HD with no backups. I saw the board was replacable, so that's what I did: bought an identical disk on eBay, some torx screwdrivers, transplated the good board to the dead disk, and it worked perfectly fine. [0] http://www.catb.org/jargon/html/M/magic-smoke.html

You were lucky that it was only the magic smoke that escaped, and not the pixie dust on the platters.

https://www.google.com/search?q=hard+drive+pixie+dust

Re: Recover HD Using a Magnet

#49
post #13

Don't use dd -- use ddrescue (reads all "working" sectors before retrying broken ones).

Does this mean it puts less strain on a potentially broken disk in an attempt to maximize how much can be rescued before it fails?

Yes.

There is also a related technique used for RAID rebuilding - SCT Error Recovery Control [0] (Western Digital's name is Time-Limited Error Recovery). The main idea is to limit the maximum time allowed during a hard drive's attempt to recover from a read/write error. Without such a limitation, when the hard drive encounters a failure, it may try rereading and remapping a bad sector and becomes temporarily unresponsive, making the RAID controller to believe that the entire hard drive has failed, and potentially put more strain on the existing disk in an unnecessary full rebuild.

[0] https://en.wikipedia.org/wiki/Error_recovery_control

Re: Recover HD Using a Magnet

#50

Clever! I'm stuck on a problem right now as well, I'm trying to boot an old server (Supermicro, dual CPU) to verify something and for the life of me I can't figure out what is wrong with it. It doesn't do anything when you power it up, even the power led on the board doesn't light up. Forcing the powersupply to 'on' does light up the LED but the system still won't boot. Already put a fresh 3V cell in it, stripped it…

Oh, did any caps blow? There were some counterfeit ones going around some time ago...

That's a good one, did not think to check that, I'll go over all the caps on the MB.
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