Multiple or single database - to mearge or not?
 

We run a network of four phpbb forums - we just bought our vb license and working towards the changeover. I would like to have all the four forums share the user sessions table so that users do not have to register or login to each forum separately.

Now according to our developer the best way is to merge all the data into one vb database and use vB Cookie Cutter to spawn the login across the four domains. I know we will require four licenses anyway but the question is: Is it better in terms of server performance to have four databases running four vb installs or merge them into one?

One of the forums gets over a 100k page view per day - the others are relatively low traffic. Kindly help in deciding which approach would be the best. Has anyone of you done this in your past?

I don't know about cross-login, I believe that it would be very risky in terms of security, but for performance purposes, as long as all databases are kept in one machine, it would be pretty much the same if you have 4 db or one with different prefixes.

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About database, is better to have 4 databases separate, less data to scan per table. How is the I/O on your database disks?