Christian have you ever thought of being a politician?
I guess its wait for the translation.
Actually SMB for me means Small to Medium Business.
I look at generally up 25 users a single server will do above I am thinking of splitting services.
If I am going higher then I think your looking into an area that already has a lot of solutions canonical has some excellent offerings here.
There used to be a time when hardware was quite expensive and this is not true to the level of a couple of years ago. You can quite a punch out of a €600 server nowadays and across 25 users the investment is minimal.
Downtime at this level is still hugely expensive for any business. So I am unsure how you can say this is unneeded?
There are solutions at all levels and sometimes they need solutions that fit the budget.
Bringing in SAN and the extra network requirements that san database storage and server start to take it out of the small and some medium business requirements. Zentyal is based on a easy to use web interface that takes techno out of the equation and I am not sure if clusters are above the scope of the project.
I am not saying that your solution isn't required but I have to argue at the level I am looking at its overkill.
If one server goes down then another server comes up. It can be achieved simply its costs are low and for many it will provide a solution fit for purpose.
I also think it would be a very simple module for the Zentyal staff to develop without need for any further technologies that don't already exist in the zentyal package.
There is no way of doing it at the moment as firstly there is no heartbeat monitor.
Secondly there isn't anywhere to apply IP addresses without them being live.
It could be quite easily provided for by two virtual eth ports being the linkage between the two servers.
Synchronisation can be scheduled so it doesn't kill the network and also database synchronisation which is zarafa's mail store. This way there is hardly any additional overhead which is not true of clustering technologies.
I shouldn't of used the terminology of cluster I am talking of a Zentyal redundant backup server that will kick in automatically on a service failure on the primary.
For many that would be fit for purpose at this level.