I will keep you informed....
2.5 hours rebuilding now. Status is still damaged and the disks are still working hard.
What has changed, is the type of the disk in the Webadmin. It's no longer marked as a spare, but a active disk
The Capacity is marked differently than the others, that might change when its done...
ID Drive Capacity Type Status
35 /dev/sda 750.1 GB, 0x0000000 GB active disk OK
36 /dev/sdb 750.1 GB, 0x0000000 GB active disk OK
37 /dev/sdc 750.1 GB, 0x0000000 GB active disk OK
39 /dev/sdd 750.1 GB active disk OK