There are some files that rapidly change. There are some files that hardly change at all. Depend on the nature of the files, I decide where to store a backup copy. You use both Windows Live SkyDrive and external hard drives to store the files that I constantly make changes. Some files, for example, your photos that were taken months or years ago, you may never want to change them. DVD-Rs are the cheapest option out there. Frankly speaking, they do occupy a lot of spaces. So I use external hard drive. Sooner or later, it may stop working. Hence, I'm thinking of replacing my external hard drives once in a few years to ensure that I won't lose any datas.