PROAR: A Weak Consistency Model for Ceph

The primary-copy consistency model used in Ceph cannot satisfy the low latency requirement of write operation required by users. In this paper, we propose a weak consistency model, PROAR, based on a distributed hash ring mechanism to allow clients to only commit data to the primary node and synchronize data to replication nodes asynchronously in Ceph. Based on the distributed hash ring mechanism, the low latency requirement of write operation can be met. In addition, the workload of the primary node can be reduced while that of replication nodes can be more balanced. We have evaluated the proposed scheme on a Ceph storage system with 3 storage nodes. The experimental results show that PROAR can reduce about 50% write overhead compared to that of Ceph and has a more balanced workload around all the replication nodes.