An information system includes a primary storage system (PSS), a host, an external storage system (ESS), and a management host. The PSS uses virtual devices to treat logical devices in the ESS as if they were logical devices in the PSS. The ESS logical devices are configured using multiple disks for providing redundancy, such as in a RAID configuration, to enable migration of data following hardware failure in the ESS. When a disk forming part of an ESS logical device fails, the management host detects the failure and judges whether the ESS logical device is used by the PSS to form a virtual device. If the ESS logical device is used to form a virtual device, then the management host issues a migration request. In response to the migration request, the PSS migrates data from the ESS logical device to a logical device in the PSS to avoid data loss.