How to get status of my Gigabyte Raid?

I have a Gigabyte motherboard, GA-X58A-UD3R, running Windows 7. I have a SSD for the c: drive but a RAID 1 array using the motherboard for my D: drive. The RAID option from the motherboard I'm using is via the "Marvell 9128 SATA Controller" (uses the GSATA 6_7/IDE Controller slots).

Has been working fine for about a year (well seemingly working fine, didn't actually pull out drives to test the RAID after building it). Has a problem now with the symptom of very slow access (really slow, takes 15 minutes to boot up, slow accessing anything on the drive - so something is really wrong, except if you wait it eventually does give you the data)

QUESTION: How do I actually check the status of the Gigabyte RAID array? i.e. how to get diagnostics, and even something as basic as an indication of whether one drive has failed? Where do I get this? If I try to run the Gigabyte RAID Configurer (whatever this is) I get "GBB36X Raid Device is not found"? Is this the software I'd need to get working to get a picture of the raid status?

Note: Going into BIOS the RAID setup seems OK. And in Device Manager there are no issues highlighted.