I heard a lot of good words by aerospike. That Aerospike eat much less memory than Redis. But I have another remarks.
Redis 2Gb Ram vs Aero 2Gb Ram. In redis I use lists, z operations, set-get and much more. In aero I use just lists.
So Redis with 2Gb RAM with 80000 elements in list eat 700MB. Ans Aero with 2Gb RAM with 4500 elements in list eat 1800MB. Aero namespace: write-block 8M, data-in-memory false. 3 dbs with repl factor 3.