When using the rsync parameter --sparse or -S to efficiently copy large VM disk images (VMDK files) you need rsync version 3.0.5 or newer as with older version you get into data corruption without any error messages during the synchronisation process!
This problem was reproduced with rsync --daemon 3.0.4 on ESX and rsync client 3.0.2 on Solaris 10 either on UFS or ZFS.
Release notes about this issued: http://rsync.samba.org/ftp/rsync/src/rsync-3.0.5-NEWS
NEWS for rsync 3.0.5 (28 Dec 2008) Protocol: 30 (unchanged) Changes since 3.0.4: BUG FIXES:
- Fixed a bug when using --sparse on a sparse file that has over 2GB of consecutive sparse data.
bug details: https://bugzilla.samba.org/show_bug.cgi?id=3925