Abstract: A technique for storing data operates a replication splitter in a host computing device. The host computing device runs an application and monitors write performance from the application to both a data storage array and a replication site. If the monitored performance indicates that writes to the replication site would not significantly slow down the application, the replication splitter operates in synchronous mode, in which the splitter waits to acknowledge writes from the application until it receives confirmation of write completion from both the data storage array and the replication site. However, if the monitored performance indicates that writes to the replication site would significantly slow down the application, the replication splitter operates in asynchronous mode, in which the splitter acknowledges writes from the application as soon as it receives confirmation that the data storage array has completed those writes and without waiting for acknowledgements from the replication site.