Probably a FAQ but I haven't found anything useful after a while of searching:
Can I set up NFS in such a way that every single error (e.g. server CPU, hard disk, hd controller, network adapter, network cable, power supply) is masked without any need for immediate intervention?
I have only answers for parts of the problem: RAID, redundant power supply, redundant network adapters
How do I address CPU failure of the NFS server so that clients fail over transparently?