According to one embodiment, a memory system determine both of a first block to which data from a host is to be written and a first location of the first block, when receiving a write request to designate a first logical address from the host. The memory system writes the data from the host to the first location of the first block. The memory system notifies the host of the first logical address, a first block number designating the first block, and a first in-block offset indicating an offset from a leading part of the first block to the first location by a multiple of grain having a size different from a page size.