cassandra read performance depends on your disk cache (free memory at
node not used by cassandra) and disk IOPS peformance. In ideal case (no
need to merge sstables) cassandra needs 2 IOPS per data read if
cassandra key/row caches are not used.
Standard hard drive has about 150 IOPS. If you have one hard drive per
machine, 50 reads per second on ~ 10 GB CFs with random key access is
about fine.
dont trust stress tool too much, it is way different from real world
workloads. In real world you will have hotspots and these will get cached.
