The primary advantage of Redis is native data types and access patterns beyond simple key-values: lists, sets, sorted sets, hash tables, pub/sub, hyperloglog, and scripting (lua) support.
Being memory-based was simply a feature but not necessarily something that set it apart: Memcached had that area pretty well locked down for being a blazing fast key-value store. And then Membase was basically memcached + persistence and clustering. Now Redis has clustering too!
seconded. memory = fast is not the point. the point is that it gives you specific data types that do specific things and since it's in memory it does those things very quickly. that said, you need to implement your own clustering or sharing solution. jury is still out on the new cluster code, i havent reviewed it yet.
Being memory-based was simply a feature but not necessarily something that set it apart: Memcached had that area pretty well locked down for being a blazing fast key-value store. And then Membase was basically memcached + persistence and clustering. Now Redis has clustering too!