The process of files getting corrupted due to some hardware or software failure is referred to as data corruption and this is one of the main problems which web hosting companies face since the larger a hard disk drive is and the more info is filed on it, the much more likely it is for data to get corrupted. There are various fail-safes, but often the information gets corrupted silently, so neither the file system, nor the administrators notice anything. Because of this, a bad file will be handled as a good one and if the HDD is part of a RAID, that file will be copied on all other drives. Theoretically, this is for redundancy, but in reality the damage will be even worse. The moment a given file gets damaged, it will be partly or fully unreadable, so a text file will not be readable, an image file will display a random combination of colors if it opens at all and an archive shall be impossible to unpack, and you risk losing your website content. Although the most popular server file systems have various checks, they are likely to fail to find some problem early enough or require a vast period of time to check all of the files and the web server will not be operational in the meantime.