In Windows, if there is a red X on a mapped network drive, follow these directions below. As an example, notice the E drive has a red X.
On the Windows server which has the drives, bring up the Disk Management window by entering diskmgmt.msc into the Start Menu search. In this example, one of the mirrored disk in the E drive is missing, thus the E drive has Failed Redundancy. The following URL has additional intel on Failed Redundancy: https://technet.microsoft.com/en-us/library/cc787481%28WS.10%29.aspx.
There are two steps to take here. First, we will want to determine if the drive itself has failed, by restarting Windows. If no issues occur when restarting Windows, the second action is to use Disk Management to mirror the drive.
To determine if the drive has failed, restart Windows. As an example, when one of my drives failed, the computer hung during the boot process for about 1 minute, and then displayed an error S.M.A.R.T. Status Bad, Backup and Replace.
If no issues present themselves during boot, return to Disk Management, and follow the steps listed here.