You have set up two hard drives so that they look like one drive in your operating system. When you write to one, it creates an exact copy on the other. What level of RAID is this?

This configuration is a mirrored drive, RAID 1. In case one drive fails, you have an exact duplicate on the other drive. You still need backups since it provides fault tolerance but does not protect your system from user error. Disk striping, or RAID 0, improves performance but has no effect on fault tolerance. Disk striping with parity, or RAID 5, provides fault tolerance in addition to performance improvement. Data is written on two drives, while recovery data is striped over the third drive. Each drive receives the recovery data in turn. If one drive fails, the recovery data on the other two drives will be adequate to rebuild it. RAID 10 provides fault tolerance and performance improvement in a different way from RAID 5 because it is a striped set of mirrors.