A package controller of a flash package, upon receiving an update data write request with respect to a first logical storage area corresponding to a first LU that is treated as a backup target, manages a first physical storage area as a backup storage area in a state where pre-update data is maintained, newly allocates a second physical storage area to the first logical storage area, and writes the update data to the second physical storage area. The package controller, upon receiving an update data write request with respect to a second logical storage area corresponding to a second LU that is treated as a non-backup target, manages a third physical storage area allocated to the second logical storage area as an invalid storage area, and writes the update data to a fourth physical storage area newly allocated to the second logical storage area. The package controller performs control so as to use the first physical storage area to provide backup data for the first LU, and delete pre-update data stored in the third physical storage area.