Yes. Although Aerospike has technology to make optimal use of SSDs, some customers have chosen to use RAM as storage. It is also possible to have data in one namespace go to RAM while data in another namespace goes into SSD all within the same cluster. Generally, use of SSDs are preferred because of the much higher data density per node. RAM should be used when object sizes are small (<100 bytes) and/or transaction throughput is critical (>100 ktps/node).