A method, a system, an apparatus for allocating a hard disk to a placement group, and a storage medium. An allocated placement group count of each candidate hard disk in a pool of candidate hard disks is acquired, where the allocated placement group count is increased by one count unit, each time said hard disk is allocated to any placement group. A table of allocated placement group counts is established based on the allocated placement group count, where the table reflects a correspondence between candidate hard disks and placement group counts. Candidate hard disks are selected from the table based on an ascending order of the allocated placement group count, to obtain target hard disks, where a quantity of the candidate hard disks is equal to a quantity of hard disks required by a target placement group. The target hard disks are allocated to the target placement group.