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Data Recovery: A Primer

PhotoFirst, let's start by stating that data recovery is mostly science. But -and we really don't like to admit this- there's a bit of art and luck mixed in sometimes. We'll get to that in a bit.

What causes a hard disk to fail? We have to define some terms here. Most people refer to any failure of the hard drive to work properly as a "crash." Actually, we define as a "crash" only when the disk's read/write heads smack down onto the disk platters' surface and cause catastrophic failure. This happens in only a small percentage of cases of drive failure. Most of the time the problem is caused by a sector or multiple sectors being unable to be read properly. This can result in a drive being unable to boot properly or hanging when attempting to access certain files. Depending upon the number of sectors involved, the prognosis for data recovery may range from excellent to questionable. A few sectors here and there will seldom prevent a thoroughly successful recovery. Large areas of sector damage can be more problematic. This damage is not caused by any action of the user. Over time, the magnetic properties of the disk surface can be weakened; small particles of residue within the drive can become lodged under a read/write head and cause microscopic damage. The bottom line is that most disk "crashes" are actually varying degrees of disk surface damage, very few of them resulting in catastrophic failure that defies data recovery.

Then there's the damage that can occur when the electronics board fails on the drive. This normally results in a no-spin condition, although there are times when it can cause other symptoms. Time was when a user could swap out the board with one from a similar model and, usually, all would be well again. With today's drives this is the exception rather than the rule. Most current drives have electronics boards that have flash ROM chips written with information that is specific to that drive only; you cannot swap the board with a similar one to make it operational. We have the equipment necessary to transfer that information to a working board and gain access to the data.

Sometimes you'll turn on your PC and find that, even though the drive is spinning and no strange noises are heard, it's not recognized at all by the system. You'll get some sort of "hard disk failure" message at startup. Often this is caused by a "firmware" problem on the drive. Firmware is information relating to specific disk characteristics which is normally stored both on the electronics board and special areas of the disk surface. This disk-based firmware area cannot be accessed without the use of special hardware and software. When one of these firmware modules becomes corrupted or unreadable drive failure of the type described here will occur. Sometimes failed modules can be copied from similar drive models but, more often, the modules are specific to your drive and must be re-built through special techniques. Micro Surgeon has the tools to effect this type of repair.

The notorious clicking sounds that accompany many drive failures are frequently caused by failure of the read/write head assembly and/or by catastrophic damage to the disk surfaces. The symptom can occur in other scenarios as well but is most often associated with r/w head failure. In this case the drive must be opened in a dust-free environment and the read/write head assembly must be replaced with a similar model. This is a highly specialized task that requires special tools and skills. Micro Surgeon can successfully perform this procedure to restore access to the data areas. In cases where the disk surface has sustained severe damage by a true "crash" the data will usually be unrecoverable. However, this happens in a relatively small percentage of cases.

Another type of problem that sometimes occurs, especially in laptop drives, is being locked out of the drive because of password issues. By this we don't mean the software password that allows you to lock out certain users from your files; rather, this is the password that is built into the hard drive itself, without which access to the data becomes impossible.

The password can be lost or forgotten by the user, or the drive can spontaneously set a password through a glitch. In either case, we can use our tools to bypass the password and unlock the drive.

Where does the art and luck enter the equation? Well, frankly sometimes a difficult drive will allow us a small window of time during which we can access the data before it totally gives up the ghost. If we're lucky enough to have extracted the critical data during that time period then we've hit paydirt. Other times, a procedural trick or some special purpose tool we design for the specific problem allows us the opportunity to get at the data.