Improve remote backup of sparse files

[lafrech]

rsync --sparse copies whole files, thus generating much traffic for a huge and almost empty VM sparse file.

Possible solutions:

• Use tar on source file:
  • http://stackoverflow.com/questions/13252682/copying-a-1tb-sparse-file
• Create an empty sparse file on remote side and rsync --inplace
  • http://unix.stackexchange.com/questions/120091/how-can-i-speed-up-operations-on-sparse-files-with-tar-gzip-rsync
  • http://stackoverflow.com/questions/19821186/rsync-sparse-does-transfer-whole-data