Prefetching data blocks from a primary storage to a secondary storage system while data is being synchronized between the primary storage and secondary storage

A computer program product for managing data synchronized between a primary storage managed by a primary controller and a secondary storage managed by a secondary controller, wherein the primary controller and the secondary controller communicate over a network, the computer program product comprises a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause operations, the operations comprising:

• determining data blocks to prefetch from the primary storage to the secondary controller not yet synchronized from the primary storage to the secondary storage in anticipation of future access requests for the data blocks to the secondary controller while data blocks are being synchronized between the primary storage and the secondary storage over the network;
• and
• sending a prefetch command to prefetch the determined data blocks to copy from the primary storage to the secondary controller to make available to future access requests received at the secondary controller for the determined data blocks.