Concurrent read/write apparatus

A magnetic tape drive includes a head assembly with a write head and a read head. The read head is positioned ahead of the write head, so that as a magnetic tape is moved across the head, the read head is able to read data that is about to be overwritten by the write head. When a client computer system commands the tape drive to write data to the magnetic tape, the tape drive writes the data to the tape but preserves any data that is overwritten by reading the data before it is overwritten. The preserved data is returned to the client computer system. In various examples, the returned data can be written back to the tape, discarded, or stored elsewhere under the control of the client computer system.