Dell PowerEdge RAID Controller 9 User’s Guide H330, H730, and H830

Break mirror in BIOS configuration utility

The RAID 1 virtual disk that you wish to split must be in an optimal state, and it cannot be running any other background tasks.

To use the Break Mirror feature, from the BIOS Configuration Utility Ctrl R, perform the following steps:

During boot up, press Ctrl R when prompted by the BIOS screen. If there is more than one controller in the system, choose the controller.
The VD Mgmt screen is displayed by default.
Highlight the appropriate Disk Group
Press F2 to display the available actions.
Choose Break Mirror and press <Enter>.
A dialog box is displayed describing the operation and asking if you are sure you want to perform the operation.
Select Yes to continue.
The exported disk (exporting configuration) spins down and the hard drive status LED starts flashing to identify which drive must be removed.
The remaining disk (exporting configuration) is in a degraded state until the missing member is replaced or rebuilt.
If there are any Global or Dedicated Hot Spare assigned, which fulfills the rebuild requirements for the degraded RAID 1 disk, a rebuild starts automatically. If there is no hot spare assigned, then an hot spare that meets all the requirements for the virtual disk must be assigned before the rebuild starts.
NOTE:Importing a broken mirror is the same as importing a foreign configuration. See Importing Or Clearing Foriegn Configurations Using VD Mgmt Menu. The imported virtual disk is in a degraded state until the missing member is rebuilt.