According to one embodiment, a memory system detects a first block in which an elapsed time from a time point at which the block has been filled with write data exceeds a first period. The memory system notifies a host of a list of identifiers capable of identifying valid data portions stored in the first block or a list of identifiers capable of identifying all data portions stored in the first block. When receiving, from the host, a first copy request specifying one or more valid data portions stored in the first block as copy target data and specifying the second block group as a copy destination block group, the memory system copies the one or more valid data portions specified as the copy target data from the first block to the second block group.