Performance with riak can't reach expected

I benchmark riak's performance using basho_bench in the last days. But the performance is unsatisfying. I have a 2 node cluster, each node running on the same vm(8 CPU, 32 GB RAM). Riak's storage_backend is memory. The total ops could reach 1 with the put command. Can I do something to make

Performance with riak can't reach expected

I benchmark riak's performance using basho_bench in the last days. But the performance is unsatisfying. I have a 2 node cluster, each node running on the same vm(8 CPU, 32 GB RAM). Riak's storage_backend is memory. The total ops could reach 1 with the put command. Can I do something to mak