Embodiments in accordance with the present invention help a disk drive to effectively cope with a data address mark detection error. In one embodiment, a data sector is provided with plural data address marks and an read/write (RW) channel reads out the data sector using part of those data address marks. Each divisional section of a split sector has two data address marks and the RW channel uses one of the two data address marks. A data address mark to be used is specified by a register. When an error occurs in detecting a data address mark, its position is stored in a register. Based on the error position, an error recovery processing section stores, in the register, a data address mark to be used in a next retry.