The process of files being damaged resulting from some hardware or software failure is referred to as data corruption and this is one of the main problems that web hosting companies face because the larger a hard drive is and the more data is placed on it, the more likely it is for data to get corrupted. You'll find a couple of fail-safes, still often the data becomes damaged silently, so neither the particular file system, nor the administrators notice anything. Consequently, a bad file will be treated as a regular one and if the hard drive 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 be worse. When a given file gets damaged, it will be partially or entirely unreadable, so a text file will not be readable, an image file will present a random mix of colors in case it opens at all and an archive will be impossible to unpack, and you risk sacrificing your site content. Although the most commonly used server file systems feature various checks, they often fail to identify some problem early enough or require a vast period of time to check all the files and the web server will not be operational for the time being.