Volatile memory devices may be on a first memory module that is coupled to a memory controller by a first signal path. A nonvolatile memory device may be on a second memory module that is coupled to the first memory module by a second signal path. A memory transaction for the nonvolatile memory device may be transferred from the memory controller to at least one of the volatile memory devices using the first signal path and data associated with the memory transaction is to be written from at least one of the volatile memory devices to the nonvolatile memory device using the second signal path and a control signal. A defect circuit may generate the control signal in view of a detection of a defect in the nonvolatile memory device based on a comparison of a test value read from a memory location to a stored value.