The process of files getting damaged caused by some hardware or software failure is known as data corruption and this is among the main problems that hosting companies face since the larger a hard drive is and the more info is stored on it, the much more likely it is for data to become corrupted. You will find a couple of fail-safes, but often the info gets corrupted silently, so neither the particular file system, nor the admins see a thing. Thus, a corrupted file will be handled as a regular one and if the hard disk is a part of a RAID, that file will be copied on all other drives. Theoretically, this is done for redundancy, but in practice the damage will get even worse. The moment some file gets corrupted, it will be partly or entirely unreadable, so a text file will no longer be readable, an image file will show a random combination of colors if it opens at all and an archive shall be impossible to unpack, and you risk losing your content. Although the most popular server file systems include various checks, they often fail to discover some problem early enough or require an extensive period of time in order to check all of the files and the web server will not be functional for the time being.