Archived from groups: rec.photo.digital.slr-systems (
More info?)
From: "DoN. Nichols" <dnichols@d-and-d.com>
| In article <1110334590.796776.279190@g14g2000cwa.googlegroups.com>,
| eawckyegcy@yahoo.com <eawckyegcy@yahoo.com> wrote:
>> DoN. Nichols wrote:
|
| [ ... ]
|
>>> Strong magnetic fields, such as might be found in various
>>> explosives detectors, X-rays, and the like, could degrade the
>>> information on the disk.
>>
>> www.google.com: magnetic coercivity
>> www.google.com: faraday cage
>>
>> All modern harddisks are ensconced in a metal box, and made from
>> magnetic materials can only be tweaked by a very strong field floating
>> micrometres from the surface. Indeed, as capacities have increased, so
>> has this natural "protection" from whatever external fields can make it
>> through the box.
|
| They may be enclosed in a metal box, but that metal box is quite
| often cast aluminum, which offers little in the way of protection
| against DC magnetic fields -- just high frequency ones, where the
| induced currents by the AC field tend to buck the incident fields.
|
| And a Faraday cage is *not* a continuous shell (as are the drive
| enclosures), but rather a set of conductors in parallel terminating in a
| single conductor. And they are good against RFI, not DC magnetic
| fields.
|
>> Some amusement.
http
/wipe.sourceforge.net/secure_del.html
>>
>> "[...] In addition, like physical destruction, it requires highly
>> specialised equipment which is expensive and difficult to obtain
>> (one example of an adequate degausser was the 2.5 MW Navy research
>> magnet used by a former Pentagon site manager to degauss a 14" hard
>> drive for 1« minutes. It bent the platters on the drive and
>> probably succeeded in erasing it beyond the capabilities of
>> any data recovery attempts [20])."
|
| Certainly the bent platters would render it unreadable by
| anything other than a data-recovery specialist -- and only if it was
| never put in a drive and spun up with the warped platters -- whether it
| was degaussed or not. And the fact that there was sufficient force to
| bend the aluminum platters suggests that there was a significant
| high-frequency component to the field -- probably at the onset, which
| did most of the work. That would have been done in milliseconds, and
| the (much less than) one minute was not necessary.
|
>>> And -- the shocks of typical mail handling systems, even in the
>>> US, would vastly increase the chances that the disks would be
>> partially
>>> or completely unreadable once you got home to where they were.
>>
>> I guess if you just mailed the disk alone attached to a post-card or
>> something. But who would do that? I've received delicate instruments,
>> expensive optics, and even HD's in boxes via courier's and the mail.
>> How many packing-peanuts has humanity made to date?
|
| And how many are available in the field -- in whatever country
| you happen to be shooting -- to ensure that the mailing is safe. I have
| heard of parts of the world where the most available packing material is
| fresh-popped popcorn -- if the local rodents don't eat into your package
| to consume your packing material.
|
>>> I would go for two DVDs -- as mentioned above, of different
>>> brands of media -- and ship *one* home, while keeping the other in my
>>> luggage.
>>
>> DVD's, CD's, are too small,
|
| Too small compared to the bulk of an external disk drive, with
| power supply? And consider the mass which you have to carry with you
| until you are ready to entrust it to the mail system of whatever country
| you are in, and the various other mail systems between the point of
| mailing and the intended destination.
|
| Or do you mean that the capacity is too low? I think that a 4.7
| GB DVD would be a pretty good match for a 4GB full CF card.
|
| Also -- how does the cost of the CF cards compare to that of disks
| in enclosures? Given the bulk question, I would be tempted to stock up
| on CF cards, and keep them all with me until I returned -- or mail each
| as it got full, and hope that those at the other end would mail back to
| you the CF cards after they were safely copied to at least two storage
| media.
|
>> too finicky, too silly.
|
| Exactly what is silly about a DVD ROM?
|
| As for finicky, I have had no trouble burning them on my unix
| systems -- though I have heard of Windows systems requiring shutting
| just about everything which is running to safely burn a CD-ROM or
| DVD-ROM.
|
>> Buy a pair of
>> 80GB+ laptop disks (I find desktops bulky, but are perfectly fine if
>> you can accept the size/weight/power consumption), enclosures for same
>> with CF ports and do the backup trick.
|
| I have had mere 6GB laptop disks die from a short drop (about 18
| inches. I have never had a problem with CF cards dropped from greater
| heights.
|
| And what do you intend to use to write the laptop disks, as the
| original poster stated that he did *not* want to take a laptop along?
|
| Enjoy,
| DoN.
| --
| Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
| (too) near Washington D.C. |
http/www.d-and-d.com/dnichols/DoN.html
| --- Black Holes are where God is dividing by zero ---
I agree with everything you said except -- "...DC magnetic fields."
It is the AC magnetic fields one must worry about because it is the constant transitioning
of North to South magnetic poles the degausses.
--
Dave
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