I’m building a cluster of Raspberry Pi computers to run Hadoop and one of the tasks that I need is to make working backups of the micro SD cards that these computers use to store their operating system. This page takes you carefully through all the steps you need to make a backup and then to restore it to a different micro SD card.
Johnny Winter. How to Clone Your Raspberry Pi SD Cards With Windows. Envato Tuts+ blog, December 27, 2013. Available at https://computers.tutsplus.com/articles/how-to-clone-your-raspberry-pi-sd-cards-with-windows–mac-59294.