CAWRM: A remote mirroring system based on AoDI volume

Nowadays, data reliability and availability are big challenges that the designers of large data centers have to face. Remote mirroring technology is an effective approach for data protection. It maintains a complete copy of primary site at geographically distant locations. Data consistency is the key point of the replication process in the remote mirroring system. This paper improves the consistency strategy of traditional remote mirroring architectures from three aspects: initial synchronization, real-time replication logic and resumption from network failure with the help of a novel logical volume, AoDI. AoDI is an Allocation-On-Demand Incremental volume. It uses an appending storage structure to provide the ability of space allocation on demand and fast snapshot. This paper presents two remote mirroring architectures based on AoDI volume. One architecture incorporates the remote mirroring logic with the AoDI structure loosely. It provides a way to construct block-level heterogeneous remote mirroring system and improves random write performance remarkably. Another architecture combines the remote mirroring logic with the AoDI structure tightly. Besides the advantages of the loosely coupled architecture, the tightly coupled architecture simplifies remote mirroring logic significantly. The remote backup process separates from normal write process completely. The remote mirroring module simply copy data sequentially from the local volume (an AoDI volume) to backup site repeatedly, so we call this architecture CAWRM (Copy After Write Remote Mirroring).