If you delete files or accidentally format a hard drive it doesn’t mean the data has gone, it just means the space where the data resides has become available to be overwritten. Data can be recovered using specialist software.
Data Loss by Malware or Data Corruption
Viruses and Malicious Code on your computer can compromise your data, it is important to backup your data regularly but if the worst happens then it’s entirely possible the data can be recovered.
Hard Drive Failure
A computers storage technology is not infallible, in fact every hard drive has a limited lifespan, on average they will last about 5 years but the reality is they could let go at any moment. I cannot stress the importance of doing a regular backup. At the very least you should store your important files on a USB stick or upload the files to an online storage resource. If your hard drive is about to fail it will often cause problems or if system monitoring software called SMART is enabled it will give a warning of impending failure. Even if your data has disappeared or the system will no longer start it is still possible that your data can be recovered.
RAID Disk Arrays and Disk Mirroring
RAID (Redundant Array of Independent Disks) is a method of data storage where data is spread across an array of many combined disk drives. This approach is usually implemented on a company file server and increases performance because data is being retrieved from multiple sources at the same time. It also incorporates redundancies, so that in the event of a hard drive failure the data on that drive can be reconstructed using data from the other disk drives in the array. This method of data recovery has been available for many years however it is becoming increasingly impractical due to the large capacity of hard drives these days. Where it used to take hours to restore data, it can now take days, so other methods of data storage are evolving such as BeyondRAID and Disk Mirroring where data is replicated on another disk drive in it's entirety. The data recovery and data security solution you might adopt will very much depend on the value and size of your data.