Why bother running RAID in a non-commercial environment. RAID is great for high availability environments in data centres, in that failures are recovered quickly when a disk fails - providing you have another similar spare disk to rebuild your data on to. The downside of RAID is that both disks are usually spinning most of the time and using disks wears them out. Also there are a lot of things that can take out a RAID array (power failure, virus, controller issues, driver issues etc.) and you can
lose all of your data.
Which is why RAID is no substitute for a backup - ever. You are already experiencing issues in just setting up the RAID on your machine which should be a warning. Many years in IT has taught me not to trust RAID and I have seen very experienced IT staff suffer at the hands of a corrupted data centre RAID array that has destroyed all of the data and resulted in a complete re-build from backups that has taken days.
A suggestion - use one WD disk as your live disk and the other as the backup drive - preferably as an external drive. The backup can be set to just backup incremental changes so you only have to copy the main data once and then after that the backup will be very small. Also this drive will only be on when you are backing up which reduces wear and tear and will give it a longer life than the live drive giving you much more piece of mind in the long run. If the main disk fails or gets corrupted for any reason you have another copy external to your machine that will have escaped the problems affecting the internal disk. Personally, if the data is that important, I would have at least two external backup drives.