Seems like I'm doing a lot of revisting these days. Perhaps I'm just not making myself clear.
I have basically five types of systems in my organization; mission critical, 24x7, ancillary, QA, and Development. Below are some detail explanations of each type of system:
A mission critical application is a piece of software that must be running in order for the business to continue to operate. Without the software, the business would cease to exist. An example of this is eBay's auction system or the software that executes orders for Ameritrade.
A 24x7 system is important to the business, but not essential for the business to run. If a 24x7 system goes down, customers get upset but business continues to operate. An example of this type of system would be Ameritrade's charts or eBay's feedback system.
An ancillary system is a system that a limited number of users access. If an ancillary system is down your bean counters may complain because they can't crunch their numbers, but overall, there is no impact to the business. Usually an ancillary system is something used internally and not exposed to your customer. An example of this type of system might be eBay's customer data warehouse or Ameritrade's accounting system.
A QA system is "almost production" in the sense that it carries a full load of production data, but the data may be "stale". Performance testing occurs on these types of systems as well as new software changes. The only people that are affected by QA outages are those running the tests.
A development system is a work in progress. A handful of developers will be ticked off if development is down, but nobody really cares.
Mission Critical, 24x7, and Ancillary systems are production systems and are treated as such. Any production system is important to the business, just some are more important than others. QA systems are sometimes treated like production, sometimes not. Development systems are almost never treated like production.
In "Where am I deploying MySQL", I point out what types of systems where I am comfortable deploying MySQL. I have deployed several systems in development, QA, and production. My production apps are mostly of ancillary type, but I have recently deployed a 24x7 web based application. As we build the infrastructure around MySQL, there will be a natural progression towards more 24x7 apps. Those ancillary and 24x7 apps eventually evolve into mission critical systems as our experience becomes deeper and our confidence becomes stronger.
I'm an Oracle guy, no question about it. But I'm implementing MySQL. In fact, the vast majority of my new systems are being developed on MySQL and are going into production on MySQL.
From time to time we have to emerge from our comfort zones. We can either confront it as an opportunity to learn and progress or fear it and fail.