The process of files being corrupted as a consequence of some hardware or software failure is referred to as data corruption and this is one of the main problems that hosting companies face as the larger a hard disk is and the more data is filed on it, the much more likely it is for data to be corrupted. There are several fail-safes, but often the info becomes damaged silently, so neither the file system, nor the administrators notice anything. Thus, a damaged file will be treated as a regular one and if the HDD is part of a RAID, that particular file will be copied on all other disk drives. In principle, this is done for redundancy, but in reality the damage will be worse. The moment a file gets damaged, it will be partly or entirely unreadable, which means that a text file will no longer be readable, an image file will display a random combination of colors in case it opens at all and an archive shall be impossible to unpack, so you risk sacrificing your site content. Although the most widely used server file systems feature various checks, they quite often fail to find some problem early enough or require an extensive amount of time to check all of the files and the server will not be operational in the meantime.