Each node in the figure represents a data node (ChunkServer). A CopySet is the basic unit of data replication in CurveBS. A CopySet contains multiple chunks. Copysets in CurveBS are created in advance advance. When users write data, they only need to select an appropriate CopySet and create a new chunk. Why use a CopySet to manage data? 1. Reduce metadata. If the replication group membership is the communication traffic between replication groups is heavy. Once a CopySet is introduced, it can be explored with CopySet granularity. 3. Improve data reliability. If the replication group is