I'm creating a site where user can register making posts using PHP. Presently I've 2 tables inside a db, and a lot of csv files. Each of them together hold, username, password etc. and counters, posts, date etc correspondingly.

My Real question is Whether it may be beneficial to choose two storage systems. Obviously i'm able to store everything inside a database. My primary problem is fast read &lifier write capacity.

Also observe that some information is needed frequently, plus some is needed rarely, if i must divide the information b/w csv &lifier db, so what can be superior way?

Only use DB, CSV isn't for your.