Memory system and method of controlling nonvolatile memory

A memory system connectable to a host, the memory system comprising:

• a nonvolatile memory including a plurality of blocks, each of the plurality of blocks being a unit of a data erase operation;
• and
• a controller electrically connected to the nonvolatile memory and configured to:
• manage a plurality of block groups, each of the plurality of block groups including one or more of the plurality of blocks, the plurality of block groups including at least a first block group;
• manage a plurality of logical regions, the plurality of logical regions including at least a first logical region;
• allocate the first block group to the first logical region for dedicatedly writing data associated with the first logical region;
• execute a first operation to the first block group, the first operation including the data erase operation to each of the one or more of the plurality of blocks included in the first block group;
• while a period elapsed from the execution of the first operation is shorter than a first threshold, in response to receiving, from the host, one or more first write requests each specifying the first logical region, write first data requested by the one or more first write requests into the first block group;
• and
• when the period elapsed after the execution of the first operation is longer than the first threshold and an unwritten region is included in the first block group, change a state of the first block group such that data not associated with the first logical region is also to be written into the first block group.