A system that stores sets of data blocks in extents located in storage devices is described. During operation, a receiving device receives, through an RPC framework, a first call asking to transfer an extent from a sending device to the receiving device. In response, the receiving device opens a port for a data connection that operates outside the RPC framework. The receiving device makes a second call, to the sending device through the RPC framework, asking to stream the extent to the port. The receiving device subsequently receives the extent from the sending device through the port and computes a checksum for the extent. The receiving device also receives a return from the second call, including a checksum for the extent computed by the sending device. If the computed checksum matches the received checksum, the receiving device returns the first call to indicate the transfer operation completed successfully.