Overnight, for no apparent reason, my work server decided to reset the bios to default settings ... erasing the raid array settings, and defaulting to ide.
When I arrived this morning, windows had helpfully "fixed" the boot drive. Urgh.
Reinstall of the OS was required, after windows recovery failed to detect the system images on both an internal hdd and the USB drive .... clonezilla system image was missing in action.
At least the data drives were intact, although the Intel raid insisted on resynching the second drive