Proposed are a storage system and its control method capable of dealing with the unique problems that arise when using a nonvolatile memory as the memory device while effectively preventing performance deterioration. This storage system is provided with a plurality of memory modules having one or more nonvolatile memory chips, and a controller for controlling the reading and writing of data from and in each memory module. The memory module decides the nonvolatile memory chip to become a copy destination of data stored in the nonvolatile memory when a failure occurs in the nonvolatile memory chip of a self memory module, and copies the data stored in the failed nonvolatile memory chip to the nonvolatile memory chip decided as the copy destination.