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From: D Yuniskis on 11 Feb 2010 13:24
life imitates life wrote:
> On Thu, 11 Feb 2010 12:32:13 GMT, Jan Panteltje
> <pNaonStpealmtje(a)yahoo.com> wrote:
>
>> On a sunny day (Wed, 10 Feb 2010 21:32:47 -0700) it happened D Yuniskis
>> <not.going.to.be(a)seen.com> wrote in <hl00kt$lc3$1(a)speranza.aioe.org>:
>>
>>> <grin> I have 5T spinning and another ~10T "off-line" (tape and disc).
>>> Not counting audio/video media.
>>>
>>> Note that an OS failure can trash your drive in half an Ohnosecond
>>> (been there, done that... opted not to buy the T-shirt). This is
>>> why I backup on tape and optical media :<
>> Yes, I have more then 750 DVDs in a alu case in the attic.
>> Some are the first DVDs that you could burn, say 10 years old now?
>> It is the backup...
>>
>> My OS does NOT trash my hd :-), it runs Linux, and I have Reiserfs with several partitions on the 1TB.
>
> Power loss does not equal HD trashing as much these days, even if a
> write operation was being performed when it happened. The most that gets
> lost usually is just the data that was being written at the time.

Who said anything about power loss? If the OS contains a bug
in the driver -- or, in my case, the disk had some funky
characteristics in the SCSI interface -- then the VTOC can get
trashed in one write.

I never investigated the actual cause. I watched the system
trash my disk (4G at the time -- but 4G disks were $1K then).
Assuming the drive had failed, I replaced it with my warm
spare. And watched that drive get trashed just as quickly.

I then rolled back the OS update and restored the image from
an offline backup learning some very important lessons:
- other things besides "disc failure" can take away your data
- have multiple backups
- make sure at least one of those backups is offline
- don't rely on DASD media for backups
Of course, there are other thihngs to be learned from this
but those were the issues I learned THAT INSTANT! :>

I know that the drive in question was ultimately added to the
"fixup table" because of this "problem". But, never sorted out
what the actual cause was (I want my tools to *work*, I don't
want to spend time *making* them work... updates, etc.)
From: D Yuniskis on 11 Feb 2010 13:43
life imitates life wrote:
> On Wed, 10 Feb 2010 13:49:55 -0700, D Yuniskis <not.going.to.be(a)seen.com>
> wrote:
>
>> <grin> We don't allow magnets in the house (way too much magnetic
>> media!)
>
> I have put hard drives, VHS tapes, Floppies, and all other manner of
> magnetic storage medium on my speakers and have never, ever had a
> problem. I have even taken magnets and tried to erase floppies and hard
> drives etc, with closely proximal magnets, and have never been able to
> erase data from them.

The magnets on most speakers are sufficiently far from the edges
of most cases. Field drops as inverse square of distance so
there's little threat from a speaker (to *media* -- you might
note that unshielded speakers near a CRT will cause problems,
especially for a very high resolution CRT!)

"Refrigerator magnets" are also no threat (to media -- usually)
since most refrigerator magnets can barely hold a piece of
paper on the refrigerator (nowadays).

Now, where do you draw the line? Do you inspect each magnet
that comes into the house and characterize the strength
of its field? What criteria do you use to determine
"this one is no threat; this one IS a threat"?

> I did own a mechanical, magnet only cassette eraser that worked
> perfectly upon completion of a dual pass thru with the cassette tape.
>
> That little sucker had an array of opposed field magnets setup inside
> it, and it was just barely a free fit on the cassette form factor.
>
> For the most part though, written data is fairly strongly held on the
> medium. A nearby field morphs it, but usually only temporarily, and
> rarely does it flip even one bit.

When I use my demagnetizer, I move to the far side of the house.
It's field is strong enough that it can support a 7" reel of tape.
Unfortunately, the only control is on/off so there is no way to
slowly ramp the field down in intesity. Apparently the sudden
interruption of current can cause a large spike/"magnetic event".

> Modern hard drives with perpendicular recording are even less prone to
> loss of as written data. Just prior to the era though, the bigger drives
> of the horizontal head orientation drives were likely more susceptible to
> a few errant bit flips.
>
> Maybe they should make a high security hard drive with magnets inside
> it on a lever such that when an emergency data erasure was desired, one
> would flip the lever over, and the spinning disc would erase within
> seconds. Then, a reformat might show a forensic examiner no old data to
> examine. Just putting a bullet through the platters works too.

You need to shred the platters if you want the data to be
unrecoverable. I'm *sure* there are semi-"photographic"
techniques used to "image" data from damaged discs -- if the
motivation is high enough. We used to do it with *tape*
decades ago...
From: Dirk Bruere at NeoPax on 11 Feb 2010 13:47
D Yuniskis wrote:
> life imitates life wrote:
>> On Wed, 10 Feb 2010 13:49:55 -0700, D Yuniskis <not.going.to.be(a)seen.com>
>> wrote:
>>
>>> <grin> We don't allow magnets in the house (way too much magnetic
>>> media!)
>>
>> I have put hard drives, VHS tapes, Floppies, and all other manner of
>> magnetic storage medium on my speakers and have never, ever had a
>> problem. I have even taken magnets and tried to erase floppies and hard
>> drives etc, with closely proximal magnets, and have never been able to
>> erase data from them.
>
> The magnets on most speakers are sufficiently far from the edges
> of most cases. Field drops as inverse square of distance so
> there's little threat from a speaker (to *media* -- you might
> note that unshielded speakers near a CRT will cause problems,
> especially for a very high resolution CRT!)
>
> "Refrigerator magnets" are also no threat (to media -- usually)
> since most refrigerator magnets can barely hold a piece of
> paper on the refrigerator (nowadays).
>
> Now, where do you draw the line? Do you inspect each magnet
> that comes into the house and characterize the strength
> of its field? What criteria do you use to determine
> "this one is no threat; this one IS a threat"?

I discovered that it's a bad idea to put a Nd magnet in the same pocket
as a credit card.


--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
http://www.theconsensus.org/ - A UK political party
http://www.blogtalkradio.com/onetribe - Occult Talk Show
From: Tim Williams on 11 Feb 2010 15:15
"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message
news:hl1bk3$k50$1(a)news.albasani.net...
>>> If you feel like experimenting, it would be interesting to see if a
>>> BFM (big fat magnet) would kill an energized SMPS wall wart.
>>
>>Hmm, depending on orientation, it might enhance efficiency.
>
> Core saturation would _enhance_ efficiency?

Ya- if it's a flyback with a simple core (I'm thinking rod core, but that's
never used, for RFI reasons), the correct polarity will prevent it from
saturating in the forward direction. This is actually used: I find a lot of
magnetized rod or bobbin type inductors in monitors. They are used to boost
the horizontal deflection supply (to allow for different sweep rates on the
flyback transformer). Hook it up one way, you get almost twice the
saturation magnetization -- hook it up the other and it just goes 'phut'.
:-)

Average supplies have a transformer with a closed loop, usually C or E. In
this case, one side would get closer to saturation, while the other would
get further away. There would still be a small advantage, because the
magnetic field under the windings is stronger than in the limb(s), due to
fringing. An external bias opposing this would force saturation to occur
more evenly (= sharper saturation?), maybe gaining an amp-turn or two (out
of ~200At total). Still, 1-2At is slightly more energy.

Now, an average forward converter, that's easy. Even without opening it up,
the steel case will saturate quickly, meanwhile the [nearly] ungapped power
transformer will saturate quite easily, so it won't really take much
external field to screw it up. Most forward converters have current
protection, so it would just shut down, unless it's a *really* cheap one, in
which case it will pop the transistors and blow the fuse (if you're lucky,
the transistors will erupt in flames first :) ).

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


From: Jan Panteltje on 11 Feb 2010 15:45
On a sunny day (Thu, 11 Feb 2010 14:15:21 -0600) it happened "Tim Williams"
<tmoranwms(a)charter.net> wrote in <hl1ogp$l4k$1(a)news.eternal-september.org>:

>"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message
>news:hl1bk3$k50$1(a)news.albasani.net...
>>>> If you feel like experimenting, it would be interesting to see if a
>>>> BFM (big fat magnet) would kill an energized SMPS wall wart.
>>>
>>>Hmm, depending on orientation, it might enhance efficiency.
>>
>> Core saturation would _enhance_ efficiency?
>
>Ya- if it's a flyback with a simple core (I'm thinking rod core, but that's
>never used, for RFI reasons), the correct polarity will prevent it from
>saturating in the forward direction. This is actually used: I find a lot of
>magnetized rod or bobbin type inductors in monitors. They are used to boost
>the horizontal deflection supply (to allow for different sweep rates on the
>flyback transformer). Hook it up one way, you get almost twice the
>saturation magnetization -- hook it up the other and it just goes 'phut'.
>:-)
>
>Average supplies have a transformer with a closed loop, usually C or E. In
>this case, one side would get closer to saturation, while the other would
>get further away. There would still be a small advantage, because the
>magnetic field under the windings is stronger than in the limb(s), due to
>fringing. An external bias opposing this would force saturation to occur
>more evenly (= sharper saturation?), maybe gaining an amp-turn or two (out
>of ~200At total). Still, 1-2At is slightly more energy.
>
>Now, an average forward converter, that's easy. Even without opening it up,
>the steel case will saturate quickly, meanwhile the [nearly] ungapped power
>transformer will saturate quite easily, so it won't really take much
>external field to screw it up. Most forward converters have current
>protection, so it would just shut down, unless it's a *really* cheap one, in
>which case it will pop the transistors and blow the fuse (if you're lucky,
>the transistors will erupt in flames first :) ).
>
>Tim

I have some expensive switch mode AC / DC adaptors... laptop, GSM, etc.
I am not gonna try :-)
I will likely experiment with magnetising some ferrite rods for frequency control.
A while back a wide range VFO with such a thing was discussed here.
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