Replicated snapshots are a different size

can someone help me to understand why a replicated snapshots is smaller then its source? i cant find any missing files but im not shore all my data was replicated. If you look at the alex data set you can see what im talking about.

Do you have different topologies on the two different pools?

USED shows actual disk space used, not the logical byte size of data. So if you need more or less RAIDz padding on one side or the other, or have otherwise differing levels of storage efficiency between the two, you should expect different values for USED between them.