storing user data in a csv file vs database

I am making a site where user can register and make posts using PHP. Currently I have 2 tables in a db, and lots of csv files. Both of 开发者_如何学Cthem together hold, username, password etc. and counters, posts, date etc respectively.

My Question is If it is a good idea to go with two storage systems. Of course i can store all of it in a database. My main concern is fast read & write capability.

Also note that some data is required frequently, and some is required rarely, if i have to divide the data b/w csv & db, what can be better way?

Use only DB, CSV is not for that.