Redis and Sirius target slightly different use cases, although they share the goal of keeping data in memory. For our use case that motivated Sirius' development, we wanted to avoid doing I/O to an external system (even a fast one like Redis) in order to simplify development by having direct access to the data in native datastructures.

Additionally, we found that we needed some custom datastructures to get the performance we needed, so providing application developer control over those datastructures was an important motivation.