Bigsync is a tool to incrementally back up a big file to a slow destination
(think network media or a cheap NAS). The most common cases for bigsync are
disk images, virtual operating systems, or encrypted volumes. It will read the
source file in chunks, calculating checksums for each one. It will compare them
with previously stored values for the destination file and overwrite changed
chunks if checksums differ. This way, it minimizes the access to slow target
media.