increasing block numbers and don't reread cylinder 0.
2. Recognize the USTAR.... meta-info file...kind of like a super-block,
it makes the volume size and label info programmable.
addressing and disk changing code. Separate disk addressing into three layers.
(virtual: ustar format space spanning volumes, logical: format space relative
to current volume, and physical: standard meaning). Compute a checksum of the
disk 0 8k label area, and define a label for disk 2, 3.... Detect incorrect
disk changing order and attempt to recognize our disk 0 from its checksum.
