rsync of block devices

How to clone virtual disks as logical volumes with resume?

Some clever folks are working on patches to "rsync" to allow the copying of block devices:  http://lists.samba.org/archive/rsync/2010-June/025164.html

Paul Whittaker fixed me up with just such a patched version of rsync so I can move my VM disks around my network more efficiently.  The only thing to note is /dev/mapper/<logical_volume> is a symbolic link and you must use /dev/<vg>/<lv> to access the real block device.  

The example below is me running an "rsync" check over a previously cloned volume that failed to cleanly complete when using my favourite "nc" (netcat) method.  A three minute verify is not bad for an 8GB virtual disk!

root@blackdouglas> rsync -vP --inplace --copy-devices jd:/dev/mapper/JD-vm_canobolissmith_ROOT /dev/mapper/BD1-vm_canobolissmith_ROOT
JD-vm_canobolissmith_ROOT
           0 100%    0.00kB/s    0:03:18 (xfer#1, to-check=0/1)

sent 741502 bytes  received 370826 bytes  3570.88 bytes/sec
total size is 0  speedup is 0.00
root@blackdouglas>