Cassandra node hardware requirement

Question

We have a lot of keyspaces, RF=3, each keyspace has ~1Gb of data. Can we effectively serve such configuration with small nodes like 4GB RAM + 60GB SSD?

Answer 1

You are missing some parameters:

1. Number of keyspaces.

2. Number of how many nodes you want to use.

3. Number of cores per node.

But, anyway:

1. 4GB RAM is kind off minimal requirement. You will be able to run nodes, but there's will no place for OS level caching, Java heap will be very small etc. Most of the best practices guides suggest using 8/16GB configuration as minimum.

2. 60GB of SSD - it depends on the amount of the data per server. If you planning to use STCS you should not go much beyond 50% disk usage, leaving us with 30GB. If you have very small data set you can live with it, but if you go higher, you should use more storage.

As a general advice, i'll suggest using servers with higher amount of RAM. It can be possible, theoretically, to run with such configuration in production, but it will probably make more problems than effort. Expect crashes, GC problems, out of memory errors, performance drops etc.

EDIT:

1. 2 CPU Cores - is very low. Cassandra using CPU heavily during compaction process, compression, if enabled, reading data (more if compressed) etc. Try to get more cores if you can.

2. 4GB RAM minimum - It doesn't depend on keyspace size, the absolute minimum is around 2GB AKAIK, but in most cases Cassandra will consume more, and regarding the fact that there's also OS running, it will be problematic to live with such a small amount. DataStax recccomend starting in production with 32GB, see http://docs.datastax.com/en/landing_page/doc/landing_page/planning/planningHardware.html

3. Having 15 servers with 60GB storage, there's will be 900GB available. 100 keyspaces with size of GB is 100GB, so from the storage perspective you should be ok :).