The process of files getting corrupted due to some hardware or software failure is known as data corruption and this is among the main problems which Internet hosting companies face as the larger a hard disk drive is and the more data is placed on it, the more likely it is for data to be corrupted. You'll find different fail-safes, but often the data is corrupted silently, so neither the file system, nor the admins notice a thing. Because of this, a bad file will be treated as a standard one and if the hard disk is part of a RAID, that particular file will be duplicated on all other drives. Theoretically, this is for redundancy, but in reality the damage will get even worse. Once some file gets damaged, it will be partly or entirely unreadable, therefore a text file will no longer be readable, an image file will show a random mix of colors if it opens at all and an archive will be impossible to unpack, and you risk sacrificing your site content. Although the most widespread server file systems feature various checks, they are likely to fail to identify a problem early enough or require an extensive amount of time in order to check all of the files and the web server will not be operational in the meantime.