Is it good idea to use RAID 1 mirroring to back up database content

I'm working on web hosting project. The planned system structure is going to be like this: - one main hard-drive will contain the binary of mysql. - A second hard-drive will contain the datadir - the third hard-drive should contain a backup of this mentioned datadir. I can only think of two options here either replication using 2 instances of MySQL servers or just using RAID 1 mirroring only the datadir. I would go with mirroring but I'm kind of suspicious of using this method and my main frightening thought is what if I lost the main hard-drive that contain the binary of mysql does setting new version will cause my a problem .. any ideas suggestions will be great full thanks I should mention that using INNODB is a constraint