In some examples, for migrating data from a first storage system to a second storage system, a system creates a proxy at the first storage system to direct write requests received at the first storage system to the second storage system, initially sets a cache in the first storage system to a first state in which the cache stores write data for first write requests, and changes a state of the cache from the first state to a second state in which write data for second write requests bypasses the cache and are directed by the proxy to the second storage system.