I have experienced a rash of failing hard drives lately. It is important to always have a good backup because hard drive failures can happen suddenly. There are several types of hard drives failures and depending on what type it is will determine success or failure in recovering data. Hard drive failures can be divided into 4 main categories: head crash, bad sectors, defective controller, and write wearing. The last one only applies to solid-state hard drives (SSD’s). When a hard drive’s motor gets old it does slow down but as long as the motor spins fast enough the hard drive is still useable; that is not a failure.
A hard drive has a few main parts: one or more magnetic platters, read/write heads, and a controller to control it all and communicate with the computer. Any failure with the read/write heads is a head crash. The read/write heads must be very close to the magnetic platter, less than the width of a human hair. In fact, if not for the air from the spinning platter the read/write head would make physical contact with the platter. Whenever you have a head crash your only recovery option is to send it off to a professional hard drive recovery service.
Magnetic platters are always two-sided. Sometimes the read/write head is jarred and make physical contact with the platter. That is a bad thing, the data where the read/write made contact is probably lost and that side of the read/write head is probably destroyed.
Sometimes the read/write gets stuck and you will hear a clicking sound. There is no way to get it un-stuck.
The data on a hard drive is divided into sectors of either 512 bytes or, on new hard drives, 4096 bytes. All you need to know about a sector is that it just a section on the hard drive that has your data and other important information about your data and that they are arraigned in a logical order so that the hard drive knows how to quickly locate it. Sometimes parts of a sector on the magnetic platter go bad. If any part of the sector goes bad then data is lost. There are programs that can recover data when there are bad sectors, but they can only recover data that is not in a bad sector. In other words, even if only 10 bytes in a sector are corrupt then all the data in that sector is unrecoverable. Professional hard drive recovery services will have the tools to recover partial data from a bad sector.
A cheaper option is to use a disk checking program found in every operating system and have the bad sectors blacklisted. This is a very slow process. After that, you might be able to browse the unaffected files and simply copy them off or you might have to use a file undelete program to recover the unaffected data. This option may or may not work depending on where the bad sectors are.
It is perfectly natural for a hard drive to have some bad sectors from the factory and still be healthy. In fact all hard drives have a little extra secret capacity that is used when a bad sector is encountered. When there are more than a few bad sectors then you have problems.
Each hard drive has must something on it to communicate with the computer and control the hard drive. Sometimes this controller goes bad but everything else is fine. If this happens, then all you need is a controller from an identical hard drive to replace. It has to be the exact same. Thus it can be difficult to find a good controller that is exactly the same. Sometimes putting the hard drive in a freezer for several hours will bring the controller back to life, although this is rare.
If a replacement cannot be found or if freezing the hard drive does not work then your only option is a professional data recovery service.
SSD’s have no moving parts, just special non-volatile memory. (Non-volatile memory is memory that retains its data after the power has been lost.) These hard drives are much much faster because they have no moving parts, but they cost much more although prices are dropping steadily.
Each memory cell in a SSD has a finite number of times data can be changed. Eventually the memory cell will fail. If the memory cell fails but the hard drive thinks it is still good, data is lost. Most of today’s SSD have algorithms that prevent the same memory cell from being used frequently. Modern SSD’s have a good wear algorithm and thus the longevity of SSD’s is as long as traditional hard drives.
SSD’s should never be defragmented because where the file is physically stored is irrelevant for these drives. There are no moving parts. The purpose of defragmenting a hard drive is to minimize how often the read/write head on a traditional hard drive moves. Defragmenting will only shorten the life of a SSD.
Professional data recovery services might be able to recover the data from a write wearing failure, but don’t count on it.