Many people will tell you that the best backup solution for the home user is to buy a second harddisk and use software RAID to implement disk mirroring. An easy mistake to make, but a mistake nevertheless. RAID only protects against hardware failures, not against software problems. If a careless user, broken application or a virus deletes important data, RAID will immediately mirror this change on the "backup copy", therefore it offers no safety against such problems (also not against theft or destruction of the entire computer).