In one embodiment, upon initiation of a consistency group, bandwidth reduction scanning logic determines whether a volume portion such as a track containing data which is to be mirrored from a primary volume to a secondary volume to form a consistency group, is allocated to the primary volume. If not, the bandwidth reduction scanning logic causes the data of the associated volume portion to not be mirrored from the primary volume to the secondary volume. As a result, the volume portion determined to not be allocated to the primary volume is bypassed by the mirroring operation, thereby reducing bandwidth usage by the mirroring and accelerating the formation of a consistency group. Other features and aspects may be realized, depending upon the particular application.