Advice sought on On-Line Strategy

I have been asked to advise on a system which will incorporate Informix On-Line over a WAN and am seeking any advice from knowledgable sources. There is a system in place at present on 4.1 which is housed across 3 separate Unix machines in 3 UK wide locations, Informix is being used as the engine for a system written in Progress and the 3 location operate in isolation and then update each other over a Kilosteam link at the end of the day. There are 30 people each at location A&B and about 15 at location C all of whom require access to the Unix/Informix system. The client has already decided to go On-Line with the backing of their software suppliers. They are using IBM Risc based Unix machines. The new system will need to be real-time and fault-tolerant, also they will be installing a DOS/Win LAN (probably Novell) in each location (with a view to accessing the Unix Systems either via Terminal Emulation or network). The software is Unix based and initial thoughts by the customer are that a Unix machine is still needed at each site to run the applications from with the data ideally being stored at one location. I would be interested to hear other peoples thoughts, would a single machine do the job - with kilostream access being used to carry Terminal Emulation/Network traffic. What are the features that On-Line has for fault tolerance and how would these best be set up (ie. they are looking to have a standby server - could we do mirroring between machines). Any advice or thoughts would be appreciated. Malcolm Edeson, UK