RAID level 1 is known as disk mirroring. Disk mirroring uses two or more hard drives and duplicates the data from one drive to the others. The fact that RAID 1 does store a second copy of the data on another member of the volume means that this solution does offer fault tolerance. Fault tolerance is the concept that if one part of the solution fails, the other guy will pick up the workload and the solution will continue to function. If one of the disks in the mirror fails, you can replace the failed disk by breaking the mirror, adding a new functioning disk, and then rebuilding the mirror from the existing disk that did not fail. Once you have reestablished the mirror, you have your fault tolerance back.
The figure below displays the concept of a mirror volume. When a user saves data to a mirrored volume, the data is written to all disks that make up the volume.
RAID level 1 (Mirror) concept.
Creating a Mirrored Volume in Windows Server
In this step-by-step you will create a mirrored volume on a Windows server using two of the dynamic disks created in the preceding walkthrough. Remember that a mirrored volume stores all the data on both members (disks) in the volume. To create a mirrored volume, follow these steps: