Storage device initiating maintenance operation actively without instruction of host and electronic system including the same

A storage device comprises a controller and a plurality of nonvolatile memory devices. Maintenance conditions of the nonvolatile memory devices are monitored internally by the storage device. Upon determining that a maintenance condition is satisfied, the storage device notifies an external host. The controller may perform the maintenance operations on the plurality of nonvolatile memory devices with little disruption to the host and assure data is reliably maintained by the nonvolatile memory devices.