Patent ID: 8806170

Claim:
A storage system comprising: a first storage apparatus comprising a flash memory module as an internal device of the first storage apparatus, the flash memory module including a plurality of memory chips to store data; a second storage apparatus comprising a hard disk drive (HDD) as an internal device of the second storage apparatus, the HDD storing data, wherein the second storage apparatus is connected to the first storage apparatus as an external storage apparatus external to the first storage apparatus; and a storage controller controlling access to the flash memory module and to the HDD, and comprising a usage table, the usage table storing a substitute area capacity per unit time required for each of a plurality of usages, wherein, for a given logical device, a substitute area capacity is allocated as a storage capacity of a storage area to be preserved as a substitute memory block, and the substitute area capacity is calculated as a product of a value of a useful life span of the given logical device and the substitute area capacity per unit time required based on the usage of the given logical device, wherein the storage controller is configured to receive access requests from a host with a Small Computer System Interface (SCSI) format, wherein, when the storage controller receives a first access request of the access requests, the first access request targeting first data on the HDD, the storage controller is configured to access the HDD with a SCSI format, and wherein, when the storage controller receives a second access request of the access requests, the second access request targeting second data on the flash memory module, the storage controller is configured to access the flash memory module with a direct access format, convert a logical unit number of a logical device allocated to the host to an address of the flash memory module if the flash memory module is an internal device, identify the flash memory module, and directly access the identified flash memory module to obtain the second data.