A magnetic recording subsystem comprises a channel unit, a magnetic recording control unit having a data buffer for temporarily storing data blocks of data transferred from the channel unit and a plurality of magnetic recording units connected to the magnetic recording control unit. When the data is stored into the data buffer, a block number is assigned to each data block. When the data is read from the data buffer and to be stored into a designated magnetic recording unit, the block number supplied from the data buffer and the block number assigned when the data was stored into the data buffer are compared, and then the data is stored into the magnetic recording unit.