Highly Available File Server

Hi,

I am looking for suggestions to create a HA File Server.  I deally It would be wonderful if 2 servers could access the same LUN.. But my understanding is this cannot be done..
Also, Ideally the server(s) would be virtual and the data on a central/single SAN.

I am open to all suggestions Virtual, OpenSource, Microsoft, CIFS shares, etc..

Thanks