freeSpace
This attribute indicates the available free disk space(in bytes) on the
disk. Free space is reduced by bad blocks (if any). If there are
different numbers of bad blocks on the disks in a dual-disk system,
the reported free space will differ on the two disks.
Moreover, due to the DOS file system internal representation of
directories and files, adding and deleting files may fragment the
disks differently resulting in some disk space wasted. A small
discrepancy (less than 1% of the disk size) in the disks free space is
considered as normal.