Got into the office this morning, and the core vmware host server is down, the mirror for the boot drive barfed at around 60% when synchronising after a power failure.
Oh well, thats what mirroring is for after all, disconnected it and rebooted. nothing. no Grub nada. After running around getting a boot disk organised, making sure grub was installed etc, it STILL didn't work.
After a bit more hair tearing, I realised the BIOS had promoted the wrong drive when i removed the dud one. Doh. Of course the data drives dont have grub on them at all.