if its bootable then boot the first disk of the set and follow the instructions.
I prefer to make a USB bootable stick -- boot from that and then it will prompt me for the location of the backup files which could be on another USB drive or another hard disk drive or partition;
If you have the backup set on another partition it should take at the MOST around 15 - 20 mins to restore your OS.
The trouble with DVD's is you have to find them, wait until prompted to swap media and there is always the chance that a DVD could become defective.
When you make system backups always have TWO in case you get some uncorrectable error on one.
The chances of TWO devices having an error at the same time are virtually negligible.