Ahmad Osama (2/5/2009)
the problem in this is that if any goes wrong with one database , others will also slow down......
How can you be certain that if one DB goes wrong, others will also slow down??
Unless all your 5 applications are inter related to all the databases.
I would go for 5 databases and the separation of applications will be done by your dev team by using different data sources or config files that use specific databases for dedicated app's.
All applications would only slow if your webserver or physical server where SQL instance is running is experiencing problems, which means even if there were 5 instances of SQL server they would slow too.
As a DBA you just propose how much space, memory and CPU might be required for all the 5 app's to run like a charm.
Rest everything you might know..like backing up and high availability of DB's to make sure app is up..
"Quality is never an accident; it is always the result of high intention, sincere effort, intelligent direction and skillful execution; it represents the wise choice of many alternatives."