I have a question regarding hardware related performance issues.

Our cassandra nodes had 4 cores with 2GB RAM and we suffered with unreasonable response time (1.5 seconds average on read for 200 calls / sec).

We then upgraded the machines to 8 cores with 8GB RAM and immediately saw an improvement (around 300ms now).

However server analytics doesn't show any peek or extra use of cpu power.

How can this be explained? does an upgrade from 4 cores to 8 cores explain such a performance boost even if it seems like the server's cpu usage is unaffected?

Thanks