According to one embodiment, a memory system is configured to operate as one of semiconductor storage devices in a storage array. The memory system includes a nonvolatile memory and a controller. The controller executes a write operation of writing data, received from a host, to the nonvolatile memory, and an internal operation for managing the memory system. When starting the internal operation, the controller estimates a value related to an amount of reduction in performance of the write operation due to the start of the internal operation, based on content of the started internal operation, and notifies the host or one or more other semiconductor storage devices of the estimated value.