Windows 8 keeps deleting files from RAID drive

Normally your BIOS, if properly configured, should have a RAID submenu you can access during boot time (it's not part of the regular BIOS setup screens). It's from that menu you choose which drives you want to be part of a RAID array and the motherboard will build the RAID 1 array before Windows even boots.

If you have RAID enabled, when it scans your drives, you should see a line with something like "press F5 for RAID options." It might be you missed that in your setup? You may have to change your BIOS POST settings to display more info during boot (i.e. turn off any "fast boot" options).

Check the manual for your motherboard for specific instructions on configuring RAID arrays for your system. If you don't have a manual, you should be able to find it online.

If it's an Intel RAID controller on the motherboard (often part of the CPU chipset) make sure you have the correct Intel Rapid Storage drivers. If it's a third party RAID controller, Google it and find out what the best drivers are.

Newer UEFI PCs behave differently than older BIOS systems did. If you're not familiar with UEFI you might want to read up it. Here's one resource: http://www.extremetech.com/computing/96985-demystifying-uefi-the-long-overdue-bios-replacement

If you're still having problems, you might also see if a BIOS update is available. But, if you've never set up your RAID array before Windows loads, that's very likely your problem.

If you're worried you have a bad drive, try testing each drive individually with the other drive removed from the system. Normally once a RAID 1 array is properly configured in BIOS it will check the drives at every boot and warn you if a drive is reporting errors.

Finally, you're wise not to try to install Windows on a RAID array. There are often headaches with that--both getting it working and down the road with things like restoring backups, drive upgrades, etc.