I don't recall exactly. It was recognized by the system, however. All operations under W7 were sluggish: mouse cursor would freeze a few seconds and then react, opening a file was quite lengthy, etc.
I stopped the pc, disconnected the eSATA drive and rebooted several times. At one point, I couldn't even get past the ASUS splash screen. Finally, after several attempts, when the ASUS RAID config screen appeared, the two original RAID disks were displayed as DEGRADED although this feature had been running perfectly for weeks. I let things run for about 6 hours (500GB disks, not full). To no avail.
When I disconnected one of the RAID disks and rebooted, the other was still labelled as DEGRADED, but everything was working fine.