A controller includes a core transferring a plurality of requests; a buffer including a plurality of clusters; a buffer manager assigning the plurality of requests respectively into the plurality of clusters, and storing storage information of the buffer and cluster information regarding each of the plurality of clusters, into which the assigned requests are respectively assigned; and a descriptor updating a descriptor report such that the cluster information regarding each of the plurality of clusters and the assigned requests correspond to each other, respectively. The buffer manager is capable of assigning automatically a request provided from a host into the buffer without a control of the core.