A method, system and program product for dynamically changing the size of a LUN in a replication based environment, the replication environment having a splitter, a production site and a replication site, the production site having a production LUN, the replication site having a journal and a replication LUN, comprising changing the LUN size on the production site based on a request to change the size of the LUN on the production site, determining on the replication site that the LUN on the production site has changed size, determining whether it is possible to change the size of the replication LUN, based on a negative determination and in response to a request for the replication LUN, pausing replication, and based on a positive determination, changing or faking the size of the replication LUN.