Question

I don’t know much about Mongodb and EC2. So as a layman, my question is how much I/O (in kb/mb/gb per second), a mongodb server can handle without choking, if mongodb server is installed on STANDARD SMALL EC2 LINUX/UBUNTU instance.

Is there any formula or software or website which can tell max strength or output of a server?

NOTE: Mongodb and EC2 instances are installed in default mode.

Thanks in advance

Answer 1

TL/DR: In our testing, an M1.Large utilizing EBS can handle (on average) about 250 non-sequential i/o operations per second. In sizing testing, this generally doesn’t get above 20-30MB per second. This is part of AWS’s “high” IO setting. For Smalls, they fall under “medium” IO, so to be safe, it would be about 1/2 to 2/3 of that output … although in full disclosure, we have not done any testing on the smaller instances.

Longer, more rambling answer …

This is a complicated question because it ultimately depends on how large your active data set is and if it is significantly more than the 1.7GB of RAM associated with that instance. The more data that does not fit into memory, the more that MongoDB will have to go to disk to get the data and the more that your app will be subject to waiting on the database as the database waits on (infamous) Amazon IO to return requested data to it.

Also, with MongoDB’s lock, if you are more subject to slower IO (i.e. inserts and updates … mainly updates), then contention could get you as well.

Also, if you don’t want to worry about these issues and be able to scale around effectively, you could use one of the MongoDB hosting services (like MongoHQ … disclaimer, I am a founder) as they allow you to scale effectively as you grow and allow you easier ways to test IO at different levels.

So, RAM and I/O performance are the important things to consider when choosing an instance.