To back up commercially made Blu ray movies, you will need to decrypt them first. At the present time, there is only one program available that is effective against the BD+ protection that is added to some Blu ray movies. That program is AnyDVD HD. It is not free, but there is a free trial to let you try out the program.
The rest of the process can be done with free tools. If your blu ray movie will fit directly onto your blank disk, all you have to do is copy the movie to the hard drive using the built-in ripper within AnyDVD HD. Rip it as an image file, then burn the image to a blank disk with ImgBurn, using the UDF 2.5 file system. ImgBurn is free to download and use.
If you only want the main movie, rip as files to the hard drive, then you can select the appropriate m2ts file within the Stream folder with tsMuxeR and have it output as a blu ray disk. Again, you will need a disk with large enough capacity to match the size of the video.
Most people will want to use 25gb disks to backup blu ray. These are much less expensive than the 50gb disks. On many, if not most blu ray movies, this means compressing the movie to a smaller size. For this you’ll need BD Rebuilder. This program is still in beta, and still free, but I suspect it will become a commercial program eventually. BD Rebuilder can compress the entire movie, or you can do main movie only backups, whichever you prefer.
Working with high def video requires a fast computer, and a great deal of hard drive space. Expect overnight encoding times, even with a quad core machine.