RAID is a method to create live backups of physical hard disks but creating RAID will decreases the usable capacity of the hard drive. Would you prefer to have backup at the cost of half of your disk...

RAID is a method to create live backups of physical hard disks but creating RAID will decreases the usable capacity of the hard drive. Would you prefer to have backup at the cost of half of your disk space? What type of RAID would be better for a home based computer setup that has frequent power failures that could cause hard disk failures?