Replication / Synchronisation

Hi Guys, my first post here for quite a while.

I have a question regarding replication and or database synchronisation:

I am doing some work on a SCADA control system in .Net - (SCADA=[S]upervision, [C]ontrol And [D]ata [A]quisition)

Obviously, these are mission critical systems that must have uptimes of greater 99%.

Tradiotionally, we have used custom written database in assembler or C, but these are getting rather long in the tooth, and, in my opinion, represent a massive man-time investment developing something that already exists 'off the shelf' (for example, our custom written database, the first version of which roled out nearly 20 years ago doesn't support SQL)

So, I'm looking to see if there is an off the shelf DB that can do what we need it to do. I lean towards Microsoft because of it's integration with the .Net platform.

However, probably the most important criteria for us is that of database synchronisation - as data from the plant arrives it is stored in a database (obviously) - however, at the SAME TIME, it is sent to a back up (standby) database which is identical in every respect, except it does not 'answer' queries, it only listens and keeps it's database up to date. Then, should the 'primary' database server fall over, the standby will become active, and it is up-to-date ready to run.

Does SQL server offer such a facility that changes to a database can be immediately and automatically 'echoed' to a standby database? Automatic promotion from standby to main is not an issue, as this decision would be taken by the application software 'in front' of the database - if it cannot contact the main DB server, it will elect to start talking to the standby, thus, philisophically (sp?) the standby is now the main server.

Hope I haven't confused anyone here with my rambling?

The problem is my hunch (not being a DB guru) is that replication is NOT what I am looking for - I *think* replication does sync data and schema (correct me if i'm wrong) but not immediately - it is scheduled? Yes?

I am looking more for synchronisation - but it has to be 'on the fly' - not every 15 minutes or 8 hours etc...

If SQL server cannot do it, then it's not a major problem, since the DB access layers of the applications themselves can simply write their data to two DB's, and queue writes in a buffer if one of the partners is offline, such that they will be written to the partner when it comes online - however, I'm all for an easy life, and if the boys at Microsoft have already settled this issue, then i'm all for that!

Your advice would be appreciated.

Regards

Mark Wills