To reconnect the disk and repair the mirrored volume
A disk containing part of a mirrored volume has been disconnected. Try to reconnect and reactivate the disk.
Make sure that the physical disk is turned on, plugged in, and attached to the computer. If necessary, turn on or reattach the physical disk.
Open Computer Management (Local)
In the console tree, click Disk Management.
Computer Management (Local) > Storage > Disk Management
Right-click the Missing or Offline disk, and then click Reactivate Disk.
If the disk does not return to Online status or if the volume does not return to Healthy status, see Replace the failed mirror with a new mirror on another disk
To open Computer Management, click Start, and then click Control Panel. Click Performance and Maintenance, click Administrative Tools, and then double-click Computer Management.
You must be logged on as an administrator or a member of the Administrators group in order to complete this procedure. If your computer is connected to a network, network policy settings may also prevent you from completing this procedure.