Data Volume degrade and missing HDD 1

I bought 6 months ago a My Book World Edition II  4TB … spent a lot of money and have had nothing but problems with the backup device.

Latest problem in the middle of the night while the pc was sleeping My Book LED’s started flasing … Data Volume degrade it says and when I look at  my WD disk manager HDD 1 is missing !!! HD 2 is there and in good condition as the status says

What  happened and what do I do now ?

I am not happy with the My Book am having one problem after another…and I seem to be NOT the only one.