A write command is received to write data in a Conventional Magnetic Recording (CMR) realm of a disk to be formatted for writing data in non-overlapping tracks. The disk includes a plurality of areas of the disk that can be formatted as a CMR realm or as a Shingled Magnetic Recording (SMR) realm formatted for writing data in overlapping tracks. It is determined whether performance of the write command would require writing to begin in a portion of the CMR realm that has not been written with non-overlapping tracks. In response to determining that the performance of the write command would require writing to begin in a portion of the CMR realm that has not been written with non-overlapping tracks, a predefined data pattern is written using non-overlapping tracks in the portion of the CMR realm that has not been written with non-overlapping tracks.