Backward compatibility for continuous read/write
From SionVersionTwo:
- Backward
- Old format should be readable
- Both, serial and parallel
- Old format should be readable
- Forward
- External tool (CLI)
For reading old files: have to keep chunksizes array(s) in file descriptor.
Design question: two read functions for old files and new files, or only old file read functions, synthesize chunksizes arrays on open for new files?