What is Data back-up and recovery?
Not too many people understand that this is is one of the most important, yet also one of the most neglected areas of computing. Backing up your data should be at the top of your computer maintenance list, right next to Virus Protection. Without data backup or virus protection, you are running the risk of losing your data. And it will happen, don't think that you don't have to worry about it.
Why should you back up?
Data loss can happen in many ways. One of the most common causes is physical failure of the media the data is stored on. You probably have everything saved on your PCs hard drive. That hard drive will not live forever. To quote a friend of mine, "there are only two types of hard drives - the ones that have failed and the ones that will fail." Yes, normally hard drives will live for years without incident. But eventually they will die. It might happen gradually, by more and more bad clusters accumulating until most of the drive is unusable. Or it might happen suddenly, the hard drive just dies without warning.
Data loss can occur not due to any physical problems with your hard drive but because it has problems accessing the data it contains at a 'software' or 'logical' level. Lets take a look at how a hard drive stores data and why it is possible to perform data recovery.
Sectors, Clusters & File Storage
When you purchase a new hard drive it is has usually already undergone a 'low level format'. The purpose of a low level format is to divide all the magnetic space on the hard drive into small storage areas. These storage areas are known as 'sectors', however for efficiency purposes the Operating System (e.g. Windows XP) groups sectors together into 'clusters'. A cluster is the smallest unit of storage space with which the Operating System will deal. If you save a very small file to your computer it will all fit within 1 storage cluster on the hard drive. If you save a very large file it may fill up many clusters, that is, as many clusters as it takes to hold all the content of the file. Things get a bit more complicated by the fact that a single file does not have to reside within contiguous clusters. It may be that the Operating System stores a single file in clusters on different parts of the hard disk. This is called a 'fragmented' file. The problem with a fragmented files is that it can slow your computer down as it needs to spend time and resources sending the actuator arm to different parts of the hard disk to read the complete file. This is why many people regularly use a defragmentation program. The amount of fragmentation in a file can also reduce your ability to recover deleted data as we will explain later in this article.
So we can now think of our hard drive as being broken down into many clusters which hold the contents of our files. A cluster that is being used to store a file is called an 'allocated cluster', and if it is not being used to store a file an 'unallocated cluster'. The next question is, 'how does the computer know where to look when it wants to find a specific file?'. Well, if you wanted to find a specific chapter in a book the best thing to do would be to go and look up the Table of Contents. A computer does much the same thing.
What should be backed-up?
You might think that you probably don't really have anything worth backing up, nothing important, no big deal. Let's go through just a few items to jog your memory.
Let's start with your favorite places on the Internet and that long list of bookmarks. Do you want to lose all those? How about the e-mail addresses from all your friends? That would take a long time to accumulate those again. What about that to-do list you wrote? Or about that nice picture somebody e-mailed you and that you saved? How about that family history you collected over the years and put into a database? Maybe you have a document for work, like a presentation or a spreadsheet that you created at home and don't have a copy on your work PC? Think about that saved game of your favorite game where it took you weeks or months to get to that level. These are just the most common examples, and I know that after thinking about it for a while you will realize that there is a lot of information you don't want to lose. That's why you should back up your data.
Another bad storage media are floppy disks. They are good for temporary storage and maybe transporting information, but not for permanent data storage. I've lost count of how many floppies I've tossed because they were bad. And I have talked to countless people who saved valuable data to a floppy only to find out when they needed to access it that the floppy was bad and the data inaccessible.
Another possible cause for data loss is power failure or spikes. It can result in loss of the document you are currently working on because you did not save it before the power failed and your PC shut down, or in loss of your entire hard drive because a power surge fried your motherboard and destroyed the file allocation table of your hard drive.
Also worth mentioning is data loss through virus attacks. There are plenty of nasty computer viruses out there that will delete files on an infected machine. That's why Virus Protection is just as important.