Can someone refresh my memory of what GeoVLAN is and what its benefits are please ?

Re: Geo VLAN

Yes.

Google can.

http://www.microsoft.com/technet/prodtechnol/windows2000serv/maintain/optimize/geoclust.mspx

Clusters of servers provide more power than any single server can provide whilst appearing to be a single logical server, and can provide redundancy to protect against hardware failures on any single machine. But a cluster of servers that are all co-located are still vulnerable to disasters like floods and malicious damage. So you want to geographically disperse them. But clustering software expects all the servers in the cluster to be on the same LAN segment. So the trick is to create a geographically dispersed virtual LAN.