The process of files being corrupted owing to some hardware or software failure is called data corruption and this is one of the main problems which Internet hosting companies face because the larger a hard disk is and the more information is kept on it, the more likely it is for data to become corrupted. You'll find several fail-safes, still often the data is damaged silently, so neither the particular file system, nor the administrators see 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 duplicated on all other drives. Theoretically, this is done for redundancy, but in practice the damage will be worse. When some file gets damaged, it will be partially or entirely unreadable, therefore a text file will not be readable, an image file will show a random blend of colors in case it opens at all and an archive shall be impossible to unpack, so you risk losing your content. Although the most widespread server file systems include various checks, they often fail to detect a problem early enough or require a long amount of time in order to check all of the files and the server will not be operational for the time being.