Howtogeek posted a guide about using drive mirroring for instant backup in Windows 7
Even with the best backup solution, a hard drive crash means you lose a few hours of work. By enabling drive mirroring in Windows 7, you always have an up-to-date copy of your data. Windows 7s mirroring which is only available in Professional, Enterprise, and Ultimate editions is a software implementation of RAID 1, which means that two or more disks are holding the exact same data. The files are constantly kept in sync, so that if one of the disks fails, you won't lose any data.Use Drive Mirroring for Instant Backup in Windows 7
Note that mirroring is not technically a backup solution, because if you accidentally delete a file, it's gone from both hard disks (though you may be able to recover the file). As an additional caveat, having mirrored disks requires changing them to dynamic disks, which can only be read within modern versions of Windows (you may have problems working with a dynamic disk in other operating systems or in older versions of Windows). See this Wikipedia page for more information. You will need at least one empty disk to set up disk mirroring. We'll show you how to mirror an existing disk (of equal or lesser size) without losing any data on the mirrored drive, and how to set up two empty disks as mirrored copies from the get-go.
