In the Neo4j world, large datasets are substantially larger than main memory. With such large datasets, it’s impossible for a Neo4j instance to cache the whole database in RAM and therefore provide extremely rapid traversals of the graph, since we’ll have to hit the disk eventually. In those situations we’ve previously recommended scaling vertically by opting for solid-state storage to provide constant, low seek times for data on disk (avoiding the high seek penalty incurred by spinning disks). While the SSD approach provides a substantial performance boost in most scenarios, even the fastest SSD isn’t a replacement for RAM. Read the whole article here.