The process of files being damaged caused by some hardware or software failure is known as data corruption and this is one of the main problems that Internet hosting companies face as the larger a hard drive is and the more information is placed on it, the much more likely it is for data to get corrupted. You'll find a couple of fail-safes, still often the info is damaged silently, so neither the particular file system, nor the admins see a thing. Because of this, a bad file will be treated as a good one and if the HDD is part of a RAID, that particular file will be duplicated on all other disk drives. In principle, this is for redundancy, but in reality the damage will get worse. Once some file gets corrupted, it will be partly or completely unreadable, which means that a text file will not be readable, an image file will present a random combination of colors in case it opens at all and an archive shall be impossible to unpack, and you risk losing your site content. Although the most widespread server file systems feature various checks, they frequently fail to identify some problem early enough or require a long period of time to check all files and the hosting server will not be functional for the time being.