One thing to note, the data change rate/replication size is going to fluctuate over time.  One large write and the amount of data to be replicated can be large.  Or someone decides to defrag a volume, now many pages on the array will be modified.  On the EQL support site there is also a KB article on why snapshots(replicas) grow, search for "snapshot size" in the Knowledge base, NOT the website search,  and it has a link to disable last access date/time in Windows.   By default, every read operation will also have a small write operation.  This can increase replication/snapshot size as well.   Or in ESX moving the swapfile location for VMs to a non-replicated volume can help reduce replication size.   
Hi,  Can anyone help me find out how to work out the rate of data change on a volume? I need to be able to work this out of SAN to SAN replication. I guess you take a snapshot and calculate the change, but where can I see the size of each snap?
Calculating the rate of change