RAID1, or mirroring, is the technique of writing the same data to more than one disk drive. Mirrors are usually used to guard against data loss due to drive failure. Each drive in a mirror contains an identical copy of the data. When an individual drive fails, the mirror continues to work, providing data from the drives that are still functioning. The computer keeps running, and the administrator has time to replace the failed drive without user interruption.

Two common situations are illustrated in these examples. The first creates a mirror out of two new drives and uses it as a replacement for an existing single drive. The second example creates a mirror on a single new drive, copies the old drive’s data to it, then inserts the old drive into the mirror. While this procedure is slightly more complicated, it only requires one new drive.

Windows 7’s mirroring – which is only available in Professional, Enterprise, and Ultimate editions – is a software implementation of RAID 1, which means that two or more disks are holding the exact same data. The files are constantly kept in sync, so that if one of the disks fails, you won’t lose any data.

In Windows 7

  1. Click on the start button and type partitions in the search box. Click on the Create and format hard disk partitions entry that shows up. (Alternatively, if you’ve disabled the search box, press Win+R to open the Run window and type in: diskmgmt.msc)
  2. The Disk Management window will appear. We’ve got a small disk, labeled OldData, that we want to mirror in a second disk of the same size. (Note: The disk that you will use to mirror the existing disk must be unallocated. If it is not, then right-click on it and select Delete Volume… to mark it as unallocated. This will destroy any data on that drive.)
  3. Right-click on the existing disk that you want to mirror. Select Add Mirror….
  4. Select the disk that you want to use to mirror the existing disk’s data and press Add Mirror.
  5. The new disk will be marked as a mirror, and it will starting copying data from the existing drive to the new one.
  6. You will be warned that this process will change the existing disk from basic to dynamic. Note that this process will not delete any data on the disk!
  7. Eventually the drives will be synced up (it can take a while), and any data added to the E:drive will exist on both physical hard drives.