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Hard Disk Recovery / Hard Drive Recovery

The hard disk in your computer is the place where the data is stored, and the data is at its most current. So, if it fails and there is not a current backup then it can be a very serious problem requiring specialist hard disk drive recovery services.

Why will a disk fail?

You have a solid platter, hence "hard" disk, happily rotating at 10,000 rpm and with a solid read/write head floating a microscopic distance above the surface. This head is mounted upon an arm that flicks backwards and forwards across the surface of the disk platter to read and write data. All this is within a small enclosed space and the whole unit is crammed inside another small space amongst a load of other heat generating components. Described like this then it sounds like a recipe for disaster.

Hard drives are actually remarkably reliable when you consider what they are and how much demand is placed upon them, but like any electro-mechanical device they will eventually go wrong.

Head Crash

Hard Disk Crash is perhaps the most well known failure term. Often the term is mis-used, "my hard disk crashed" is a description given to just about any hard drive failure. Head Crash is when the head touches the surface of the platter, this could be the result of an impact or a mechanical failure within the HDA (HDA is the Head Disk Assembly which comprises the head/platter combination).

If the hard disk heads contact the recorded platter then the consequences are not difficult to imagine, picture the farmer lowering the plough blade into the soil and what happens then. At the point of contact the recorded surface of the disk, the actual recorded material that coats the platter, will be stripped away. There will almost certainly be damage to the heads and the hard disk drive will no longer operate.

Media Failure

Anyone looking at the file system on a DOS formatted disk when MFM and ESDI disks were in vogue will remember seeing entries in the File Allocation Table that marked file system clusters as bad. Hard disks were even supplied with a list of sectors that had failed during testing so that these could be mapped out from use.

Modern disks do not come with "bad sectors", well actually they do. What modern disks do is to retain a selection of sectors as spare, these are then used as substitutes so if, during writing a hard disk sector, a failure occurs then the disk will map that sector out and use one of its spare sectors in its place.

Over time the number of failed sectors on a disk may grow, but these are mapped out and you don't see them. These will come a point when the number of failed sectors outstrips the spare sectors available, usually once a disk has started into a steady decline, and read errors will start to be reported from the drive.

The chances are that instances of bad sectors will start to be found within the most commonly used areas of the disk and these will cause problems with access to the file system and suddenly you can no longer access some or all of the data.

Electronic Failure

Hard disks are electronically sensitive devices and vulnerable to static, power supply problems and general component failure that "just happens".

A failure in the drive electronics will simply stop the disk in its tracks, if it won't spin it won't work. There are, however, more subtle electronic failures that can result in a disk spinning up but then failing to yield data, these are discussed later in this article under "memory failures".

Alignment failure and head failure.

The ability to position the heads precisely above the point where the required data will pass by is essential for the correct operation of a disk. Mechanical wear can lead to problems with the ability to position with adequate precision, especially as the density of recording on hard disks is increasing at an astonishing rate.

If any of the read heads within the drive fail, and can no longer turn the magnetic signal going past into something that can be decoded by the drive electronics then again the disk has failed.

In either of the above instance the drive will attempt to correct for the problem by entering a retry process, it might have the occasional success, but the trend will be ever downwards towards an eventual total failure.

Bearing seizure

10,000 rpm is pretty fast and the rotation has to be smooth and precise. Within the hard disk are a set of bearings that allow the required rotation to be maintained. If the bearings start to fail then the disk will become noisy and performance might fall off as the level of vibration impacts upon the ability of the drive to alight the heads over the correct data. If they fail completely then the disk will be silent and non-operational.

Memory failure

Hard disks store vital operational information both in memory devices on the disk controller and within private data areas on the disk platter.

When a disk is powered-on one of its first operations is to load critical operational data into on-board memory, this data includes defect management maps and data translation information. Without this the data being present and correct the disk cannot function properly.

Any failure of one of the on-board memory devices, or a corruption of the code and data stored therein, can result in a disk failure.

Worse still, as some of the information stored within the on-board memory devices is created during the formatting of the drive, it is unique to that drive. This precludes simple "board-swapping" operations for many hard disk drives.

Data Failures

Often blamed on the disk, but not fairly, as you can see the hard disk is a pretty amazing device to keep working the way it does under such pressure and with so many potential points of failure.

As a computer user the operation of the disk is not something much considered so long as all is well and the files you stored can still be recovered from these disk. The reason you can store data and retrieve it is that there is a file system (FAT or NTFS with Windows, HFS for MAC etc.). The data space provided by the disk is organised into a filing structure, information is stored about the names of files and the locations used to store data for them.

If there is some failure of the computer system, or the operating system that cause this information to be corrupted then either the entire file system or sections within it can not longer be accessed. Not usually the fault of the disk.

Data Recovery

The first thing to remember is that you rely on a single thing, then getting let down can be catastrophic. If all of your data is one a single disk, and no copies kept elsewhere, then when (not if) it fails the problem is very serious.

Data Recovery specialists, such as Altirium, can work with disks suffering from any of the problems described herein and usually achieve a high level of success, but the more complex the work the higher the cost, and the more serious the failure the more likely that there will be some permanent data loss.

Whatever statistics you see claimed about 95% fix rates, what you need is your data recovered and even our most experienced recovery experts cannot replace the recorded surface where it has been stripped by the heads, or undo an over-writing process that has replaced some critical data.

Hard drive data recovery is an option, but by having adequate backups it can be an option you do not need.

Last Updated (Wednesday, 17 June 2009 13:27)

 
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