Write pacing

A system for controlling the pacing of host data writes in response to changing system conditions allows for the use of variably controlled delays that facilitate asynchronous replication with bounded lag and smooth steady-state performance. Adding delay to the writes slows down the host and dampens activity spikes. A first storage device receives a write request, transmits data to a second storage device, and acknowledges the write request. An amount of additional write response time is controlled between when the write request is received and when the write request is acknowledged by the first storage device, where the amount of additional write response time is controlled according to system parameters including an amount of lag time between when the write request is received and when the write request is committed at the second storage device.