rsync strange behaviour

[pagani laurent]

I found the explanation. It is the last of your flags with does the trick :

 --protect-decmpfs
              The com.apple.decmpfs extended attribute is  hidden  by  default
              from  list/get  xattr  calls,  therefore normal attempts to copy
              compressed files will functionally decompress those files. While
              this  is  desirable  behavior  when copying files to filesystems
              that do not support HFS+ compression, it has serious performance
              and  capacity  impacts when backing up or restoring the Mac OS X
              filesystem.

              This  option  will  transfer  the   com.apple.decmpfs   extended
              attribute  regardless of support on the destination. If a source
              file is compressed and an existing file on  the  destination  is
              not  compressed,  the  data fork of the destination file will be
              truncated and the com.apple.decmpfs xattr  will  be  transferred
              instead.  Note that compressed files will not be readable to the
              operating system of the destination  if  that  operating  system
              does  not support HFS+ compression. Once restored (with or with-
              out this option) to an operating system that supports HFS+  com-
              pression, however, these files will be accessible as usual.

              This option implies --fileflags and —xattrs

without it, a number of compressed files are decompressed in the rsync process. This explains the size expansion!