An external hard drive is an unreliable backup system
Norman Datarecovery repairs damaged hard drives. During the first quarter of 2008, the company noticed that the number of damaged hard drives had tripled in comparison with the first quarter of 2007. The problem is mostly related to cooling. Unlike their internal brothers, most external hard drives do not have a cooling system. Because many users often leave them running for hours on end, they overheat. Other frequently observed problems are malfunctions due to wrong connections to the power supply, dropping the machine or moving it too often. Some numbers indicate that 13% of external hard drives already break down during their first year of service.
So don’t use an external hard drive as your sole means of backup. Think of Murphy’s law and use a supplementary backup system, like e.g. Online Backup. COMBELL offers automatic online backup as from 5 euros per month.