Since I got a large number of interesting and
amusing responses, I'm posting a summary. I've
included 43 responses. They range from amazingly
knowledgeable and detailed to funny anecdotes
(see #6 below for the best one, and the last
comment, #43, is a great laugh). While some
people have used NMR magnets for wiping magnetic
tapes and floppies, few use them for hard
disks. The consensus is that the hard disk would
not be useable because moving parts would be
magnetized, and many felt that a static field is
not good at erasing the data. General conclusion: use a sledge hammer.
Original query:
Someone in our IT department has a large number
of hard drives that he needs to "wipe" clean of
all information. Apparently this is a
time-consuming process using a computer, and he
wondered if he could just "walk" the hard drives
though the stray field of one our magnets. I
told him that 1) it might quench our magnet and
2) it might not wipe the hard drive, but it got
me to wondering if anyone out there has tried
this novel method. At least it would be worth a
laugh if anyone had any anecdotes to share!
My anecdote is related: a woman was interested
in magnetic fields for "healing" so I asked her
to sit in the stray field of our unshielded 500
and tell me what she was experiencing. She sat
down and immediately reported an "aura" and lots
of "energy" (funny, I've never felt
anything). Then she told me she had seen images
of Jesus and Mary appear on photos that were
already developed. OK, I've had enough, I got her out of the lab.
As for the hard drives, my answer is still "not with my magnets!".
Responses:
1. Tell the person to get a sledge hammer or
borrow one and use the demolition method. Our
IT dept has a special box with a door that you
put your drive into and then you pull a
lever. The disk is demolished beyond
repair. A crow bar or sledge hammer would do as
well. I used the device on my accumulated hard
drives and would never bring any of them near the magnet.
2. If your IT person wants absolutely clean hard
drives, I think the only way is a computer
program that overwrites everything with
rubbish.Exposing them to the magnetic field might
incompletely erase the information and also might
magnetize parts of the drive that are not
supposed to be. This would render them useless for further use.
If they want to trash the drives a metal shredder
will do just fine. If they want to reuse then
only proer scrubbing with a computer will do.
3. I had a flurry of requests for magnetic healing about 15 years ago. The
requestors seemed to match your "patient's" profile then as well.
4. i have no sweet "Jesus" story, but i routinely
use my horizontal, wide bore 4.7 to wipe
drives. i just bring 'em into the faraday cage
and stick them to the dewar, usually during a
fill when i am otherwise bored. then, back to
the owner all clean and not very functional.
previously, we were instructed to put a bullet
through the drives, but, of course, guns are not allowed on campus...
5. We did an experiment a couple of years ago on our unshielded 400 and
shielded 500 on a 3 1/2 drive and a 5" floppy. The data on both were not
affected by the fields. I would assume that a hard drive would be
similar. I have had a USB stick in my pocket several times and the data
was still intact as well.
6. I could hardly resist when I read your anecdote.
We have a lady in IT who claims she is sensitive to everything. Well,
my computer in the NMR room was having problems and she was the one
on-call that day. She came down and sat down at the computer desk and
asked me if I felt a pull towards the magnet. I told her no, I felt
nothing. A few minutes later she speaks up and tells me that her head
is being pulled towards the magnet. Obviously, I asked her if she had a
metal plate in her head fearing that maybe we were dealing with that.
She took offense and told me that she had nothing in her head. She
spent another 20 minutes claiming the magnet was trying to pull her head
off and then left telling me that in the future I need to turn off the
magnet if she is expected to fix computer issues. I couldn't help it,
after she walked out, I laughed until I cried. And yes, she still
sometimes has to come if the computer freaks out, but I now assure her
that I have turned off the magnet so it won't pull her head off.
hahahahaha :) :)
As for wiping hard drives, I tried wiping one of mine but didn't have
any luck.
7. When I was still running a lab, I would occasionally reformat an old
drive, then wave it under the magnet "just to be sure." It was one
drive at a time, and it was "my" magnet. But I never tested what the
end effect was, either. Was there really less risk from passing the
drive on after? Who knows . . .
Anyway, I concur with your decision.
8. He would be better off using a high power rare
earth magnet since those can be had up to 5000
Gauss. Also if he intends to reuse the drives
I'm not sure whether this might permanently
damage the drive. If he needs to destroy the
media then a well placed ball peen hammer blow does the trick everytime.
9. I've wiped magnetic tapes this way but haven't tried harddrives.
10. It's not that novel. We've done it here and at my previous job on many
occasions (>100). It's fairly standard here when our IT people need to
dispose / permanently erase information from a disc. I usually wave it
under our 600MHz magnet for 10-15 seconds and that's been sufficient. We
have never had any adverse problems with the magnet after doing this.
The IT people have indicated that they can no longer mount / access the
drives after the procedure.
Just my 2 cents.
11. Long back I used to wipe my floppies that way. But they got erased only
when I almost touch the magnet (unshielded 300) with the floppies. I have
never tried hard disks!!
12. I tried it once a more than a decade ago with an unshielded 300 and (I
think) an old data backup tape, or maybe a floppy?... My memory fails
me, but I remember that it took a few tries. Eventually it became
unreadable, unwriteable, unusable. Trashed.
13. I tried this for an IT friend a few years
back. We waved a couple of them around just
under the probe of an unshielded 300
wide-bore. He then tested them and found that
although some data was destroyed, there was still readable data on the drives.
The technique did work well for erasing audio cassettes however!
14. I would be curious to see what a degausing
coil could do to a hard drive, since we used one
to 'degauss' the rebar in the concrete floor after we moved a magnet.
15. I have used NMR magnets to erase the formatting from 3.5" floppies for
the Zymark SMS sample changers, but never tried a harddrive.
16. We have two unshielded magnets in close enough proximity to produce a
zero gauss area. Perhaps your friend would like to visit this special
area. I would be willing to arrange a visit for a nominal fee.
17. Your unshielded 500 probably has a stray
field big enough to do the job, especially at the
top or bottom of the can. I have cleaned several
in this way using a 4.7 Tesla 33cm bore
horizontal imaging magnet and a big piece of
plywood to keep the drive from "diving" into the
bore. It wipes off the sector marks too so the
drive doesn't know how fast it spins after that,
so the drive is trashed after that. Hold on REAL tight!
18. I've see devices that can erase hard drives and such. Check out this very
long link:
http://images.google.com/imgres?imgurl=http://store.storageheaven.com/ProductImages/v91hddlt_300x300_R.jpg&imgrefurl=http://store.storageheaven.com/vs91hddltmanualharddriveandtapeeraser.aspx&usg=__E80sd_YpI1siEwZ073om7TqbVK4=&h=300&w=300&sz=75&hl=en&start=129&um=1&tbnid=eVc_gC95qcbBaM:&tbnh=116&tbnw=116&prev=/images%3Fq%3Dhard%2Bdrive%2Beraser%26ndsp%3D18%26hl%3Den%26client%3Dfirefox-a%26channel%3Ds%26rls%3Dorg.mozilla:en-US:official%26hs%3D3Jb%26sa%3DN%26start%3D126%26um%3D1
I'm not 100% but I think the important thing is the B field needs to be
fluctuating.
19. You can wipe a drive out in less than 1 min.
by using fdisk, a prg. in dos or linux os.
Someone I know tried to use a supercon only to
have the drive stuck on the mag. Fdisk will wipe
out the FAT tables very quickly, but you have to do it in terminal mode.
If you have a linux os, type sudo fdisk -l to
list the devices. It will either display
/dev/sda1 or /dev/sda2 etc. If for example it
displayed /dev/sda1, than type sudo fdisk
/dev/sda1 to run a interactive session with
fdisk. With the propmpt displayed, you can use
any of the commands listed by typing 'm'. By
typing 'd' you will be asked for the partition
number. It will be either 1-4. Select the one,
and after you hit the return key the drive will be deleted.
20. Degaussing of magnetic storage is typically
done by applying an oscillating magnetic field to
the object which needs to be "purged". Entering
a static magnetic field has very little effect on
storage devices such as hard drives and credit
cards. Even if you were to turn the device on
and let it rotate in the field, the magnetic
gradient across the rotational volume of the disk
would be substantially less than the gradients
applied during a magnetic degaussing with an
oscillating field. This is why credit cards are
not wiped when you accidently forget to remove
your wallet from your pockets. It is not too
bizarre for me to have my debit card in my shirt
pocket and find myself tuning my widebore 400 MHz
Solid state probe. I've never lost a card. I'm
not a proponent of this, but, I no longer lose
sleep over forgetting them in my pockets either.
21. One could take this towards the silly side
and have someone run towards your magnet and away
from your magnet at velocities what would emulate
a 60 Hz oscillating magnetic
field. Alternatively you could approach the
problem by applying physical shock to the device
and simply drop it on the floor a number of times
to induce degaussing that way.
22. One last note of experience, a number of
years ago, we were reviewing the possibilities of
tablet PC's in the labs. The reasonable question
came up about the devices and the NMR labs. We
all know that PC's work fine in the fringe
fields, I've had 4 PC's positioned at ~5 Gauss
for the last 15 years with no noticeable impact
on the PC performance. In this specific case we
wanted to know how close we could get to the
instruments and how destructive getting close to
the instruments was. Simply put, once you get
too close, I would estimate 15-30 G the device
turns off. I'm guessing that this power
termination is a safety feature of the system
once it notices that the hard drives are not able
to rotate any longer. Once the device was
removed from the field, it powered back on
without any noticeable effect other then the OS
complaining that the system had not been shutdown
using its normally. We repeated the test 2-5
times and the text tablet PC was used for about a
week after that with various other people before
the project review was completed.
23. The hard disk drives can be wiped by
moving them briskly in the strong field at the
top or bottom of the dewar, but it must be done
carefully. The disk platters alone are no
problem, but the motor and actuator in the drive
will be strongly attracted since they incorporate
strong permanent magnets. I'd be inclined to
allow it if the IT person is willing to
disassemble the drives and wipe only the platters
(it only requires a few minutes per drive).
I have used this method on floppies (no
strongly magnetic materials) and it works very
well. It actually works better than using a wipe
program on the computer as it leaves no remnant
magnetization at the track edges, and removes the
formatting and servo tracks as well.
The easiest way to destroy the information
is to shred the drive; perhaps you could refer
them to the grounds department to see if they
have a tree chipper. This would be the preferred
method, and no disassembly is required.
24. Hmmm....I am wondering...Are you sure, it
is not actually you who is seeing this 'aura'
with all the years of 'magnetizing' where you
have conjured up this woman by the side of your
NMR desk (you know, like Avatar !), who, not
surprisingly, is having an aura of her own ?! .... ...just kidding.
Ok, I have seen this episode in Mythbusters
where Jeremy and the other guy tried wiping off
dummy credit cards using an electromagnet and
they went upto 1000 Gauss before the card was
actually garbled ! I will say, like the '8 cups
of water a day' recipe, the reason we go bonkers
about letting anyone inside of the 5 Gauss line
is mostly due to the fear of lawyers. So, in my
opinion, wiping hard disks may not be a viable
re-employment even for abandoned NMR magnets,
leave alone for the living ones. On the other
hand, as you pointed out, anything that can add
even a theoretical risk of quenching the magnet
is not worth the trouble. I think you made the right decision.
25. We tried it some time ago with a hard disk in
the lab. The disk was probably erased but it was
also broken! Apparently there are some parts in
the whole mechanism that should not be magnetic
and putting the disk under the magnet magnetized
them and broke the whole thing. The disk was
making a very funny “clunk-clunk-clunk” sound
after this treatment while it was attempting to
spin and it was not working at all. Somebody said
that you will need to low-level format it after
that to recover it but we were not very
optimistic after the weird sound so we did not
try it. Moreover it would have taken as much time
as a real format so in the end there was not time benefit;-)
Make sure that you use a non-shielded magnet for
this, if you want to try it: Shielded magnets do
not have enough stray field to wipe out a disk
and, of course be careful not to have it stuck on
the magnet. I do not think that there is a danger
to quench the magnet if done slowly and carefully but I cannot guarantee this.
26. The stray fields on supercons almost
certainly are not large enough. He needs to get
hold of a strong horseshoe (or other permanent) magnet to run over the drives.
27. Dear Neil: this lady is certainly a good laugh! I doubt the hard
disks would quench your magnet as the iron/steel content on the disc
is pretty little. But don't try if you are not 100% convinced.
I heard that only rapid motion in the field can erase magnetic
information. I have accidentally took my cell phone and credit card
close to the magnet many times and luckily never got any harm.
28. Ten years ago some workers put steel
waterpipes few meters under my 300MHz old
unshielded magnet. We lost the field for two
weeks, and we considered new cryoshims setting.
I think, "not with my magnets !" is a very good answer.
29. I once tried to wipe a hard drive that way and found it was remarkably
inefficient, even with an unshielded 500. The drive could be booted even
after several minutes in a stray field that should have exceeded 100
gauss. Surely a hammer would be a faster method of irreversible
denaturation.
We did a big lab renovation a few years
ago where we crated an existing
magnet for a few weeks while work was going on all around it. Repainting
the room was one of the last steps. The painter claimed he had been
suffering with insomnia for about 5 years, but he started sleeping well as
soon as he came to work in our room. This made me wonder if
"magnetotherapy" might command higher hourly prices than NMR.
30. We probably all know that floppy disks (of
all types) are easily and reliably wiped clean if
they get within a few inches of an unshielded 500.
I tried the same thing with both Zip (100 & 250
MB) and Jazz (1 GB) disks a while back, and was
amazed that I could still reliably read the
contents of them even after they had been up
against the dewar can (of the same unshielded
500). I had to wave them for quite a while (~30
sec) right against the bottom of the magnet (near
the bore) to erase them (the Zip and Jazz
disks). (I had initially assumed that their
higher data density would make them easier to
erase, but that was clearly not the case.)
I also erasing a bunch of floppies at the same
time, so that verified that the magnet and my
technique were OK, and made for a fair comparison.
Sorry, I don't have any data for encased hard drives.
31. There might be a fair bit of magnetic
material (motors, etc.) in the drives. While I
think the possibility of a quench would be
remote, the possibility of one of the drives
getting out of someone's hand and being sucked
into the magnet is quite real. The likely place
for it to go would be right into the probe base or shim set (Murphy's law).
Do they want to re-use these drives? Or are they
being scrapped? I'm not sure about modern
drives, but older drives used to contain "servo
tracks" that no data was written on, but that
contained information for head positioning and
sector addressing, etc. If you erased these as
well, the drive might become
unusable. "Formatting" the disk may not re-create these tracks.
In any event, if what you want to really do is
demagnetize the surfaces of the disk an AC field
would be much more effective than a DC field
anyway. This is what they used to use for bulk
erasing of magnetic tape, and you could even buy
"bulk tape erasers". We used to use one to
demagnetize the parts of our consoles around the
old style CRT displays to get a better display.
32. I use the old 600 to bulk erase the DLT tapes
all the time. Erases them completely.
Using an unshielded big magnet like the 600 will permanently damage hard drives
however because in addition to erasing the data,
it also erases the servo track.
If you are planning on throwing the drives away afterwards, then it works very
fast. You have to get it as close as possible to the bottom of the magnet where
the probe is. Rotate twice in each direction.
Not going to quench the magnet. At least it has
not quenched the magnet yet, and i've
been doing this over 10 years. Only way to erase hi-coercivity tapes.
33. Many years ago, there was a person who worked
at the TV studio (across the hall from our NMR
room) that would erase video tapes by setting
them on the floor under the (400) magnet. It
apparently was very effective. I believe the
cartridges were plastic and there was no
indication of any effect on the magnet.
34. Now that I think of it, I do have an
anecdote. We had a student change a sample on
our unshielded 500 while wearing an old-style
"iPod" type personal music device with a hard
drive. The unit gave a good whack against the
magnet Dewar as the field pulled it in. Didn't
hurt the magnet, but the iPod was toast. Not
sure if it was the field or the impact that did it in.
35. I have wiped several hard drives past my old
400 unshielded magnet. The magnet sees it as just another small metal object.
36. My tale on erasing magnet information was
some years ago I was asked if my magnet would
erase large magnetic tape cassettes. I said yes
and two girls showed up the following morning
with two hand trucks each with a stack of several
cardboard boxes full of magnetic tape cassettes.
They started to wipe each tape cassette
individually but I suggested that all they needed
to do was to hold each side of the box to the
magnet and the box contents will be erased. After
several minutes they had completed the stack and
disappeared. A few minutes later two new stack of
boxes arrived and I then asked how may more boxes
of cassettes needed to be erased. The answer
surprised me and explained why the two girls were
so interested in using this technique to bulk
erase these tapes. Their bulk eraser could only
do one tape at a time and the number of tapes to
be erased filled the box of a full size pickup
truck. These were tape backups of medical records
and their computer system had been upgraded to a
more convenient backup system. I got a box of
nice chocolates the following week for the magnet time.
37. >She sat down and immediately reported an "aura" and lots of "energy"
Might have been the metal in her dentures and
certain articles of clothing. Or her hairpins.
>As for the hard drives, my answer is still "not with my magnets!".
Good for you !
Oh and by the way...
Neil, I have a sledgehammer and it would make
life so much easier for me if I could pick up my
rivets with it, can I swing it around your magnet to get a bit of charge?
While something as low mass as a disk drive
probably wouldn’t cause problems if one had a
very secure grip, why take the chance?
It’s akin to using the tip of a precision
micrometer to drive screws – doesn’t do such a
good job and you might end up breaking something important.
Back in the good old days of floppy and zip
disks, what I found from both personal experience
and the experience of researchers was that
wandering around an unshielded magnet with these
things in your pocket often didn’t zap them
immediately, but often caused trouble within
about a month. To this day I tell researchers
that if they are absent minded and forget
something with magnetic media (nowadays it’s
iPods), they should back it up ASAP. But
sometimes for whatever reason, the media stays
fine. So playing “Millennium Falcon vs Darth
Vadar” with the hard drives in the field may or
may not work well (depends if the force is with you – ouch)
Why not use the tool that is supposed to work –
and that every well equipped NMR lab should have
(but usually doesn’t) - a degaussing ring?
It demagnetizes objects - such as analog watches
worn by forgetful researchers that go in a bit
too close to the field, past the colorful chains,
past the scary warning signs, past the yellow &
black tape strapped on the floor ... Then they’re
late because the magnetized watch starts running
slow. The degasser always fixed the watches.
Also the degasser makes fun buzzy noises when you
press the button. The way you use is cool also –
you wave it around in circles about the object
and I suppose if you get frisky enough you can
don a mysterious looking robe and a tall pointy
hat and mumble incantations to help it along.
I never tried it on a disk though. Or an NMR magnet
Oh, maybe you could suggest a sledgehammer. I
heard it works very well to erase disks plus you
save on gym membership should there be a
sufficient quantity of drives that require
erasure. Unless the drive is to be used again
that is. (Hint: best used outside far away from NMR facilities)
38. Hi, why not trying?
Do you really believe that the magnet shall quench??
I do not, if you 'll do it slowly (walking through the strong stray
field), and if you take care for having sovereignty that they do not stick
onto the magnet.
Maybe that the drive will not work after this procedure, because the
mechanic parts (read/write heads) are magnetized, but the information on
the disc maybe is still there.
This is an interesting test, because for the case it works, you may launch
an enterprize!!
39. That gave me a good chuckle......I too have
had some oddballs snooping about recently
regarding 'other' properties of magnetic fields.
Regarding hard discs......I agree with you, keep
chunks of metal away from your magnets as in
effect from the magnet's point of view this is
all it is. I too have my doubts if it would
indeed 'clean' a hard drive and if anything just corrupt some of the data.
It would be interesting to hear if anyone has
actually done this intentionally so a summary would be good to read.
Harddrives that contain sensitive
information(credit card numbers etc) should be
"cleaned" using software, even if this takes a long time.
Some of our IT people then take harddrives to the
workshop and drill holes through them and then
ask me to place the harddrives next to my
magnets(400s and a 500).....no quench yet.
One example of a student placing his laptop too
close to the 400, which caused the failure of the
laptop(I have no direct evidence that this was as
a result of damage to the integrity of the data
on the harddrive - though this is my suspicion).
40. We have erased tape many times hard drives
should not be a problem. Just be vary careful as that is vary ferromagnetic.
Make sure they secured so they are not pulled
into the bore. Do one at a time.It can be a hazard if not carefully handled.
I hope they never want to use the drives again
the high field will make them totally unusable.
Best method to destroy the drives is to drill a hole though it.
Hope this helps.
41. If they want to use the hard drives again, then I would not subject them to
external fields like from an NMR, because this might magnetize parts, cause
head crashes, etc.
If they want to render the hard drives fully unusable, I would recommend
using either an EPR magnet, a ball peen hammer, or a bench vise.
I think you are correct in keeping them away from your unshielded 11.7T
magnet, as there is no way to turn off the field easily if ferromagnetic
parts become stuck in the magnet. The EPR magnet would be nice because you
can ramp the field up and down at will.
In the area of wiping tapes, a colleague of mine (Mark Wall, you know him, I
believe) put some old computer tapes up to one of our unshielded 11.7T
magnets and the pull was quite strong. The case was plastic, and I don't
think ferromagnetic screws were being used to keep the case together. That
is, the material in the tape itself was what the field acted upon.
Another interesting anecdote had students growing plants in the fringe field
of a magnet (~50G). No unusual behavior, so the aura perturbation must have
been minimal.
42. I've tried de-magnetizing strips on student
IDs. This didn't work, even with sitting the
card at about 100 gauss (400 MHz unshield- placed
against the side of the magnet).
Why don't they try a neodymium permanent
magnet. It has a lower magnetic field, but you
could get the drives much closer to the magnet.
Static erases some credit cards. I wonder it
they try zapping the disk with a Vandegraf
generator. It would be a charge!!! ; )
43. I'd use a splitting maul instead.
He wouldn't have global warming Emails on the drive, would he?
Neil
Neil E. Jacobsen, Ph.D.
NMR Facility Manager
Department of Chemistry
119 Old Chemistry
1306 E. University
University of Arizona
Tucson, AZ 85721
520-621-8146
FAX 520-621-8407
Received on Wed Jan 06 2010 - 09:17:43 MST
