Improving storage device efficiency during data replication. An asynchronous data replication process is initiated between a source computer and a target computer over a network. Performance of the target computer and a storage device of the target computer is monitored. At least one portion of data stored on the source computer is identified for the data replication, wherein the at least one portion of the data is organized in a data block. Whether to modify a size of the data block is determined, based on the monitored performance of the target computer. Responsive to determining to modify the size of the data block, based on the monitored performance of the target computer, the size of the data block is modified.