The process of files being damaged because of some hardware or software failure is referred to as data corruption and this is among the main problems which hosting companies face since the larger a hard drive is and the more info is kept on it, the more likely it is for data to get corrupted. You can find various fail-safes, still often the data becomes damaged silently, so neither the particular file system, nor the administrators detect a thing. Thus, a damaged file will be handled as a standard one and if the HDD is a part of a RAID, that file will be copied on all other drives. In theory, this is done for redundancy, but in practice the damage will get even worse. Once a file gets corrupted, it will be partially or completely unreadable, therefore a text file will not be readable, an image file will display a random mix of colors in case it opens at all and an archive will be impossible to unpack, so you risk sacrificing your site content. Although the most popular server file systems feature various checks, they often fail to find some problem early enough or require an extensive period of time in order to check all files and the web server will not be functional in the meantime.