A memory system connectable to a host includes a nonvolatile memory and a controller. The controller is configured to generate one or more virtual storage regions each of which is associated with a virtual machine running in the host, using physical memory regions of the nonvolatile memory, maintain a threshold value for each of said one or more virtual storage regions, determine a cumulative amount of data that have been written in each of said one or more virtual storage regions, and restrict writing of data with respect to a virtual storage region for which the cumulative amount exceeds the threshold value.