Possible causes of this issue are as follows:
- Hardware vendors have a different method of calculating storage capacity from that of the OS. Hardware vendors use decimal notation to calculate disk capacity, in which 1 GB = 1000 x 1000 x 1000 bytes. In the OS, the capacity is calculated in binary mode, in which 1 GB = 1024 x 1024 x 1024 bytes.
- The system contains hidden partitions, such as the boot partition, system backup, and restoration partition.
- The file system consumes some disk capacity. Before using a hard disk, the OS partitions the disk and initializes the file system. The configuration also occupies a small amount of disk capacity.
- The RAID array occupies some disk capacity. For example, If two 600 GB hard disks form RAID 1, only 600 GB capacity of one disk can be used.