Hi Peter,
Assuming all configurations and checks are done, then both cases could work, although the multicast traffic might make MultiSite a challenge.
Case 1 ) depending on the type of changes to the file (we can perhaps compare the two files) dedup should work well in this case. Compression will also have a chance to compress the stream.
Case 2 ) Depending on the size of file and how the changes are made, dedup might still be able to work e.g. Zlib buffer size is about 32K, depending how the changes affect the zip file, it is still possible for dedup to work on the unchanged data if zipped segments compress exactly the same. The chances that dedup will work efficiently is much lower. Depending on the compression used, wanos compression will be 0 to minimal.
Potential problems:
UDP needs to be configured very specifically: e.g. source and destination address
Since its Multicast, only the source ip is available.
Multicast destination address is going to confuse MultiSite.
Need to check the MTU of the server to avoid fragmentation.