Represents a disk for storing files.
Returns the absolute path of this disk.
Find the # of blocks available using df.
Parameters : block_size (default 1024)
Find the number of bytes taken by data downloader (i.e. the sum of the sizes of the files on disk.
When called as a class method, prints the usage across all disks. When called as an instance method, prints the usage for this particular disk.
Note that this is not the _actual_ usage (as reported by "du") but rather the sum of the sizes of the files.