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Answer to FAQ
Your Question:
What is a "head-crash" & how can it result in
permanent loss of my hard drive data?
Our Illustrative, Pictorial Answer:
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The unique "photo essay" following below on this webpage gives an excellent way of visually observing — to the extreme level — the terminally progressed, end result for one of the most common modes of hard disk drive failure and the concomitant, permanent loss of stored data that typifies the outcome. These pictures give instructive and tangible insight into the why's and wherefore's about disk drive operation and failure, and make obvious the answer to a question frequently asked of data recovery service companies such as MicroCom. The narrative makes plain the reasons behind such irreversible data loss, and describe what can potentially become the ultimate demise for any failed hard drive.
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Four spinning disk platters with mirror-like data surfaces and eight (8) read/write heads in flight (one on each side, all not visible). |
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Background: The Air Bearing
It's all about what we call the "flying head dynamic" of disk drive operation. This dynamic is an essential, functional feature that relies upon an air-bearing created by high air pressure induced between the opposing surfaces of its spinning disks and sliders containing the drive's read and write elements. What happens after an air-bearing fails and permits a head to cease its flight and come crashing down, literally, onto the incredibly delicate magnetic medium on the spinning disk surface below, is the story we're telling here. They are not supposed to happen, but if a hard drive is operated long enough and keeps spinning long enough, it's not a matter of "if" — it's only a matter of "when" — head-crashes will happen, and permanent data loss may result. Most hard drives have multiple heads, and they fly independently, one over each side of each disk. At the first moment any head touches a disk platter surface, immediate
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damage takes place at the specific physical location of contact and the drive is then in a failure mode. If valuable data had been recorded at that same spot, it is gone. No data recovery company is able to extract usable information from any physically damaged area of the recording medium.
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Disk drives derive their name, as most computer aficionados know, from the fact that the user's data is stored upon platters otherwise known as disks. The information stored by these devices, i.e. your data, is recorded magnetically on extremely rigid, perfectly round, perfectly flat, perfectly smooth platters. The platter substrate itself must be absolutely and completely NON-magnetic. During the manufacturing process, platters are coated with a microscopically thin, and hence extremely delicate plating which is a highly efficient magnetic material. This plating, while very delicate, can remain stable for many, many years, as long as nothing disturbs it by making physical contact.
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Electro-magnetically controlled "heads" (called R/W heads, for "read"/"write"), located at the end of the arm-like structures capable of positioning the heads anywhere over the disk platter surface while it rotates, are the tiny elements that go into action every time you, the computer user, want to (1) save (or "write") some information, or subsequently, (2) open (or "read") previously saved information. These R/W heads never touch the platter surfaces where your data is written, they actually FLY (like an airplane) over the surface, at a very low altitude of only about two-millionths of an inch (give or take, differs between different drive models), never making contact as long as everything is working OK. Information, your data that is, is communicated across this space, to and from the disk drive heads and the media on the platter surfaces, by means of a transmitted magnetic field.
The substrate platter material used by all disk drive manufacturers requires an extremely smooth and rigid substance. The material of choice is most commonly an aluminum alloy metal, but special glass is also used. As shown in the image at right, the magnetic coating plated onto platter surfaces appears mirror like (since the early 1990's*), and it stays that way as long as nothing touches it physically. The shiny coating is completely opaque, so after production is complete the underlying platter is not visible, therefore glass and aluminum platters look identical. NOTE: The photograph includes a screwdriver (not part of the drive mechanism, of course) only to enhance perception of the high reflectivity characterizing an undamaged disk platter surface.
The Aftermath of Disk Drive Head-Crash
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So now we get to the point of all the background we've covered above. This sequence of pictures is unique and especially interesting only because the subject disk drive was designed and built using glass platters. As everyone knows, glass is transparent. It is indeed the transparency of the disk substrate that makes this pictorial exposé so dramatically much easier to visualize and understand. With an aluminum substrate, given the opacity and similarity of color between the aluminum metal and the silvery magnetic coating, it would becomes quite difficult to revealingly portray this story photographically.
Above left the subject hard disk drive is shown before disassembly — a familiar sight to most people who have opened a desktop computer system box.
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Perhaps not so easy to see in this photograph, unless you're accustomed to disassembling hard drives (note to self: if I value the recorded data on a hard drive — I WILL NOT engage in disassembly outside the confines of a certified cleanroom — I will call MicroCom Worldwide Data Recovery!).
Obliterated Data
In a disk drive with recoverable media, the disk surface looks like a mirror (see above). Here, not so much. What you see to the right is an extreme example of a non-recoverable hard drive. Any usable data that had ever been stored upon this drive prior to this catastrophic failure has now been thoroughly obliterated.
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The photo here at left makes it quite a bit more than obvious. In the platter now removed from the drive's spindle motor assembly, the opaque, mirror-like magnetic coating the disk had on it when it was new, has been not simply scratched, but completely scraped off over most of its surface — on both sides of the disk. You can see right through it! There remains, in the
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area nearest the hole, vestiges of the magnetic material, showing dark in this image, which though damaged, was not completely dislodged form the surface of the disk substrate.
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With all of the drive's platters removed from the unit (this model was designed with ten R/W heads and therefore had a total of five platters which, by the way, is the maximum quantity of disks that it is possible to fit within a 25mm/one-inch high standard form-factor hard drive such as this one), we can now easily see inside the platter compartment.
Notice the gray colored material coating the perimeter and bottom of the circular area. The gray is actually a dusting of loose particulate matter, the silvery substance that previously formed a perfectly mirror-like recording medium. It has been scraped from the surfaces of the disks as they were spinning at high speed with the R/W heads crashed down and rubbing upon them, no longer flying normally without making contact. Deposited as "magnetic dust" all around the place where the platters had been is the very same material that previously held the data the user of this drive had stored upon it. Underneath the dust in this area is the same black-anodized aluminum drive body casting visible also around the periphery and outside the unit.
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The close-up here inside the platter housing shows a finger wipe to demonstrate the looseness of the unbound dust deposited as well as the black color of the metal casting lying underneath. The flying head dynamic of hard drive operation demands that all moving parts are kept pristinely clean, and so are sealed within a compartment to prevent contamination from all of the airborne particles floating around within the air we routinely breathe
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and pay no mind to. Such particles, even microscopic ones, were they to get inside the sealed compartment, would cause heads to crash rapidly. All of the ten R/W heads in this drive did not crash at the same time; it began with just one of the heads failing to fly. As soon as contact between the first crashing head and the disk occurred, a little "sand-storm" of magnetic dust began accumulating inside the sealed compartment. Eventually, over probably a few hours, this dust accumulated to the point where one by one it precipitated the crash of all the other heads. On average, disk drives will operate continuously without a problem for about three years. Nonetheless, some units go non-stop for over ten years, while others go down in less than ten hours! Head crashes cannot be predicted.
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Crashing - One by One
As mentioned above, the drive model in these pictures has five platters and therefore ten R/W heads (one for each surface). As mentioned also, only one of the heads crashed at first. However, if a drive continues to spin after the first crash (which, obviously, this one did), microscopic particulate matter (a.k.a. dust) is produced by the unintended friction resulting from physical contact between the no longer flying head and the rapidly spinning platter surface it was once flying over. This particulate matter becomes like a sandstorm taking place inside the sealed area inside the hard drive, spinning around at high speed along with the platters, and in a short time the contamination of the once immaculately clean environment is fouled to such extent that ALL of the other heads come crashing down. Since the drive illustrated in this pictorial continued spinning for several hours after all ten heads had crashed, all of the platters show the obvious results of the friction, wherein almost all of the plated-on magnetic material has been worn or scraped off from both sides of each disk by the R/W heads. As is easy to imagine, the delicate heads themselves were also destroyed early on in the process.
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This same head-crash process can happen with any disk drive, and it happens without regard to whether the disk platter substrate is made of aluminum alloy or glass, but with the low contrast between the silvery color of aluminum and the plated-on silvery colored magnetic medium, it is not so obvious to the untrained eye as is the case pictured
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above on this webpage. By virtue of the glass platter substrates used in the design of our subject drive, the devastation is dramatic and very much apparent. Clearly (wink), all five of these platters received ruinous levels of surface damage.
Data Turned to Dust
Dust that used to be computer information: a heavy circular coating of transmigrated magnetic dust, similar to what we saw (above) inside the platter compartment, also adhered inside the lid of the drive in the area that had been positioned over the platters (shown at right). Notice the finger wipes in two places high-lighting the accumulation of "soot" which could be viewed as the erstwhile data of this drive's user — now chaotically disorganized and hence forever lost.
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Hard Drive Melt
By the time the friction-free, cushioning air-bearings that cause the hard disk drive R/W head sliders to fly had failed in each and every case, all ten heads of this drive applied a drag against the rotation of the platters. This drag increased the torque load upon the spindle motor to a point where it got increasingly hotter and finally broke down. Due to the intense overheating precipitated by this catastrophic storage device failure, disintegration of the hard drive is evident even on the exterior of the device as adhesive material used in the drive manufacturing process, light-blue in color, melted and oozed out from the bottom of the drive.
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The Hard Disk Drive: Amazing Example of Human Ingenuity
Highly evolved air-bearing technology is now and has always been, ever since its invention, essential to the fundamental operation of all makes and models of hard disk drives. This The flying head dynamic is a physical, mechanical phenomenon that facilitates the massive storage of computer data with, by far and away, a greater combination of speed, capacity, and cost-effectivity than any other innovation for data storage to date. The high-technology electronic circuits and precision mechanics of today's low-cost hard drive is almost unimaginably more complex than the already unimaginably complex disk drives made forty years ago, machines that cost tens of thousands of dollars then. Arguably a majority of a disk drive's fabricated elements, developed by means of ingenious, ongoing, generational, evolutionary design engineering progress, are focused on supporting the stability of this one dynamic. This tiny flying head phenomenon makes possible the personal storage of a volume of data so huge as to be unimaginable by large corporations only forty years ago.
The computer hard disk drive is an amazing example of human ingenuity, but as users we must never forget the wisdom of Paul Simon: "Everything put together, sooner or later falls apart".
* Prior to about 1990, the magnetic coatings used on disk platters were an oxide or rust color.
Photography courtesy Ken Sallot, University of Florida, April 22, 2003
Narrative text written by S.E. Fowler / Steve Fowler / Stephen E. Fowler, © 2010, All rights reserved.
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