Disk array device, disk array controller, and method for copying data between physical blocks

According to an embodiment, a disk array controller includes a data copying unit and a physical block switching unit. The data copying unit copies the data from a master logical disk to a backup logical disk so as to make the master logical disk and the backup logical disk synchronous. When a second physical block assigned to the backup logical disk, corresponding to a first physical block assigned to the master logical disk is switched to a third physical block, the physical block switching unit assigns the third physical block to the backup logical disk before the data is copied from the first physical block to the backup logical disk.