A plurality of tape drives writes a plurality of indicators corresponding to a plurality of data units on a tape, wherein an indicator indicates which tape drive of the plurality of tape drives has written a corresponding data unit on the tape. Each of the plurality of tape drives generates an extent of read errors, in response to reading the plurality of data units written on the tape. The extent of read errors generated by each of the plurality of tape drives are aggregated at a computational device coupled to the plurality of tape drives. A determination is made at the computational device of a defective tape drive of the plurality of tape drives from the aggregated extent of read errors.