In order to mount your RAID configuration to your computer, you need to create a logical volume. This can be done by using the Disk Utility on your computer. To begin this process, you need to have already created an array and virtual disk from the LaCie RAID Manager. If these steps have already been completed, go ahead and open your Disk Utility, located in the Utilities folder of your Applications menu. Once open, you should see the virtual disk you created showing up in the left hand column.
Select the virtual disk line from the left hand column then go to the Partition tab on the right hand side. You will see a pull down menu that says Current, click this and select 1 Partition. Format should say Mac OS Extended Journaled. Click the Options button.
Select the appropriate partition scheme, which will most likely be GUID. Once selected click the OK button to return to the Disk Utility window. Click the Apply button from the bottom right corner. A warning message will come up, click Partition to complete creating the logical volume.