Raid 1 Mirroring

I have a My Book Studio Edition 2 that I have formatted for RAID 1 Mirroring.

I assume It’s working as when I click on info it shows the capacity as 1TB as opposed to 2TB when formatted for RAID 0 Stripping. 

It could also mean one of the drives is not working! Is there any way of checking that the mirroring os actually working?

In RAID 1 mirror mode the capacity is reduced to half of RAID 0 mode. Click About RAID tab for more info .