How much RAM and Hard Disc is recommended for my mongodb server setup

Question

I have the below scenario for an alert notification application, for which we are going to use mongodb.

Number of writes per day 20Mill

Data size of 1month data 150 GB

index(default primary index) size of 1 month data 15 GB

I want to keep the data of 12 months. How much RAM and Hard Disc is recommended for my application. I will add the additional memory that need to accomodate the working set.

Answer 1

The physical memory used by mongodb depends on the data being accessed. MongoDB only loads into physical memory data that is "touched"/required. Else even though the entire database is memory mapped it is not loaded into RAM (virtual memory vs resident memory). The actual RAM used is determined by the number of OS pages required for the data/index that you use based on queries/commands etc..

The following link has some information on this:

http://www.mongodb.org/display/DOCS/Checking+Server+Memory+Usage

If you are going to be storing approximately 165g per month and need to retain that data for a 12 month period, then you are looking at the need for at least 2tb, possibly more especially if the numbers are growing beyond what is stated above.