We've been using Mrsync for about 1 year to move blocks of data around our clusters. I'm quite pleased with the utility, although it could use some additional features.
We found early on that it the multicaster needed to be on the same subnet as the recieving hosts. We adapted the code to allow a user defined interface for hosts which existed on more than one subnet for this purpose.
Currently, we find that the software needs the ability to allow mulitple multicasts to run simultaneously. This will require the multicast address and perhaps the port to change for each multicast running.
Overall the performance is not all that bad, sending 100GIG to about 300 nodes equipped with 100MB connections takes about 8 hours. When dropping to only a small number of nodes 15 GIG to 6-10 nodes in 25minutes.