Despite the reliabilty of current hard disk recorders from Zaxcom and Sound Devices even the best machine that is perfectly maintained can have an unexpected failure. Minimizing downtown and data loss is the hallmark of a professional audio person. This can be accomplished fairly cheaply and easily as well on any budget. As with most back up equipment it doesn’t have to be as good as your primary piece of gear it just had to work. As an example if you have a Sound Devices recorder then a Tascam HD-P2 is an excellant low cost option. Or if you already have a computer and audio interface then a low cost program such as Boom Recorder may be the best option for you. It all depends on budget and your needs, which is why dealing with a professional audio retailer instead of a big box store is always better. They are an invaluable resource to you in problem solving and purchasing advice.