RAID originally stood for Redundant Array of Inexpensive Disks. It was a way of writing data across a series of cheap disk drives such that if one drive failed, the data would not be lost. This entailed duplicating some data, hence the term "redundant." In later years the phrase was reworded so that Independent replaced Inexpensive. This was largely a marketing exercise designed to stop people thinking of RAID as a cheap, and thus low-quality, storage solution.
One big problem with this system is that it works on the basis that drives will usually fail at effectively random times. In reality, it’s not uncommon for multiple drives in a RAID set-up to fail in short succession. This is a particular problem if the drives come from the same original production batch.
Most people using a RAID set-up tend not to have as rigorous a back-up scheme as with standalone drives. That’s mainly because the costs of backing up the individual disks in a RAID set-up can outweigh the savings of using RAID in the first place. This means users will likely have to rely on RAID data recovery in the event that enough disks are damaged to affect the entire system.
There are two main types of damage which RAID data recovery aims to rectify. Logical damage is when a problem, most commonly a power outage, cuts off a disk midway through writing data. This means the pattern of data on the disk will not match-up to the structure the computer expects, which can cause it problems in handling and reading the data. This usually requires a software-based solution in which a program analyzes the data and figures out how it should be correctly arranged.
A second type of damage is physical, usually when the surface of a hard drive is damaged in some way. The RAID data recovery techniques designed for such damage include attempting to replace the minimal amount of the disk surface to make the drive readable again. This will almost always mean some data is lost, but the process is designed to retrieve as much as possible. Another technique is to use special programs which can collect all the data which remains on the drive, even that which isn’t accessible by a standard operating system, and then compile it into a disk image file. This can then be written to a new drive which will be as close to the original as possible.
When you use a RAID data recovery service, check carefully to see how the pricing structure works. In many cases, the cost can vary widely depending on how widespread the damage is and thus how much work is needed to restore the data. For this reason, it is usually best to use a service which offers a free assessment and quotation but does not begin the recovery process until you have agreed a price.