Data is stored on a primary storage system and a copy of the data is stored on a secondary storage system. A determination is made that a connection between the systems is currently unavailable. Location data is maintained that identifies where changes have been made to the primary storage system while the connection is unavailable. Another determination is made that data has been lost at the secondary storage system. Recovery data required to repair the lost data is identified. Another determination is made that the connection to the secondary storage system is now available. The location data is updated with the locations of the recovery data. The secondary storage system is updated with data from the primary storage system as defined by the location data.