US Patent 11494111 Data operation based on valid memory unit count

A memory device includes a plurality of groups of memory blocks, each group including a plurality of blocks, and each block including a plurality of memory units. A memory controller for the memory device performs operations including maintaining a count of valid memory units in the group for each group and maintaining a count of valid memory units in each block of the memory device. The operations further include selecting a first group based on a count of valid memory units and the first group including a target plurality of blocks. The operations further include selecting a first target block from the target plurality of blocks, determining whether the first target block is to be erased, and erasing the first target block in response to determining that the first target block is to be erased.