A common external storage device is connected to the first and second
storage systems. The management computer comprises a capacity expansion
volume migration section that migrates a capacity-expansion volume that
the first storage system comprises to the second storage system; a host
connection path switching section that switches the host connection path
being used from a first host connection path that links a migration
source capacity-expansion volume and the host computer to a second host
connection path that links a migration destination capacity-expansion
volume and the host computer; and an external connection path switching
section that switches the external connection path being used from a
first external connection path that links a storage area allocated to the
migration source capacity-expansion volume and the external storage
device to a second external connection path that links a storage area
that is allocated to the migration destination capacity-expansion volume
and the external storage device.