Arcus is data caching cloud developed on Memcached which is a memory-based Key-Value repository. It was developed meeting requirements from various NHN services. Arcus is capable of having up-to-date cache server list of clients using ZooKeeper and also able to possess cloud architecture flexible to add or delete caching servers while eliminating extra network latency between client and server. Furthermore, to support save/ computation function of data collection which is becoming a requirement among many services, it provides list, set, b+tree structures. http://sdec.kr/