The world of data recovery is a big mystery for most consumers and even some IT professionals. This is largely because hard drives themselves are complex devices and their technological specifics are not generally well known. Data recovery companies thrive on their customers’ lack of information and often get away with charging obscene rates for any recovery, regardless of complexity.
A bit about Hard Drives
A computer hard drive stores data on metal oxide platters which spin up to 10000 revolutions per minute. An actuator arm contains the ‘head’ which reads and writes the data in the form of magnetic charges one millionth of an inch above the surface. Any given drive can have multiple read and write heads and each head can ‘crash’ independently. A head crash occurs when the read/write head comes in contact with the platters of the disk (more on head crashes below). As manufacturers strive to cram more space on hard drives without increasing their physical size, the data gets written increasingly closer together, making for very difficult recovery should one or more heads crash. The brain of the hard drive is its controller board and this is unique for each individual hard drive. One other detail worth a mention is the service track of a hard drive. This is an area located on the outer part of the disk platter and it contains the drive’s firmware zone. The firmware of a hard drive is the information used by the computer to communicate correctly with the drive. These are the main components that make a hard drive work, now let’s talk about what can go wrong.
There are many ways in which a hard disk can fail
Hard drives are extremely fragile and can suffer failures in many different ways, leading to a loss of data. The five most common types of drive failures are: logical errors, mechanical failure, electronic failure, firmware corruption, and bad sectors, or any combination these. Least severe of these is usually data loss due to logical errors.
Logical errors are often the simplest and sometimes the most difficult problems to deal with when recovering data. They can range from an invalid entry in a file allocation table, a simple problem that needs little work; to severe issues such as the corruption or loss of the entire file system. Logical errors can be spotted when files become inaccessible, there is a delay in starting up the computer, and programs do not run properly. Logical errors are often seen as simple because there is nothing wrong with the physical drive leading users to try recovering it themselves by using third party software. This is quite risky, however, as running such software on a damaged drive can result in total loss of data. The most effective way to prevent logical errors on your hard drive is to regularly use the Disk Defragmentation tool in your operating system.
Recovering a drive with logical errors can be simple and quick, however if the problem requires manual bit-by-bit reconstruction of the data, it can also be quite complex and time consuming. Normally, logical errors are in the lower end of the price range as they do not require manual disassembly of the drive, however there are cases when logical failures end up in the higher end of the price range. The bottom line with logical errors is the sooner they are caught and the less a user tampers with the drive, the better the chances for a quick and thorough recovery.
Mechanical failures are often much more serious than any other failure and frequently lead to a partial or even total loss of data. The most common type of mechanical failure is a head crash, which is when the read/write head comes in contact with the disk platter. Head crashes can be caused by a variety of reasons, including physical shock, static electricity, power surges, and mechanical read/write failure. Mechanical failures are detected by a constant clicking or grinding noise coming from the drive. If you suspect mechanical failure, you must immediately shut down your computer and call a data recovery company for advice.
Mechanical failures are usually the most severe and most challenging to recover from. All mechanical failures require physical disassembly of the drive. The replacement of a read/write head is one of the most complex and costly procedures that can be performed by a data recovery engineer, especially with larger capacity drives. The chances of recovery depend entirely on how much damage the drive has sustained, however they can be quite good. A crashed head does not mean that all your data is lost! Once again, the sooner you catch a mechanical problem and turn off your drive, the more of your precious data is likely to be rescued.
Recovering data from physically damaged hardware can involve multiple techniques. Some damage can be repaired by replacing parts in the hard disk. This alone may make the disk usable, but there may still be logical damage. A specialized disk-imaging procedure is used to recover every readable bit from the surface. Once this image is acquired and saved on a reliable medium, the image can be safely analyzed for logical damage and will possibly allow much of the original file system to be reconstructed.