GC can absolutely cause a server to get marked down by a peer. See https://support.datastax.com/hc/en-us/articles/204226199-Common-Causes-of-GC-pauses

As for tuning again we use CMS but this thread has some good G1 info that I looked at while evaluating it: https://issues.apache.org/jira/browse/CASSANDRA-7486

Also Al's awesome tuning guide has some stuff, although its 2.1-centric so might not be 100% applicable https://tobert.github.io/pages/als-cassandra-21-tuning-guide.html

On Tue, Feb 14, 2017 at 1:57 PM, Pranay akula <pranay.akula2323@gmail.com> wrote:
On couple of servers  when cassandra service is down all i see only GC pauses and load on these servers is not high when pauses happend, i haven't found any thing else is that can be the reason or do i need to look at something else ??

We are using G1GC any reference on how to adjust G1GC settings, as we can not set New Heap in G1.