RAID 1: Disk Mirroring uses one controller and a minimum of 2 hard drives. Both of the hard drives need to be the same size, but if they are not then they need to be partitioned to the same size. An example would be if you had a 30GB drive and a 40 GB hard drive.
The mirror set would contain two hard drives at 30GB each. 30GB would be for data while the second drive would be a mirror image of the data. If a hard disk were to fail then a new drive could be installed and the mirror image would be taken from the good drive. If the controller fails you are out of luck.
