Here are the steps to perform when you need to change the current datastore where the master copy (replica) lives:
1. First with the scenario stopped rename the existing VMDK files on what is the old datastore.
2. Next rerun the virtual platform settings wizard and update the datastore and any other settings that have changed. This setting is on the properties tab for the virtual appliance host, under "virtual machine":
3. Once the new datastore is selected and you have completed the wizard save the scenario and then start it with the default method of sync. It should only take a minute or so for RHA to create a new set of VMDK files on the new datastore, once it does you can now stop the scenario again.
4. Now pick any VM (you can use the virtual appliance if you want) and attach both the old and new VMDK files to it. After that you can now manually copy the data from the old VMDK to the new one, to do this we recommend using the xcopy command.
xcopy [source] [destination] /E /C /H/ R
5. When the copy is complete next detach all the VMDK files and restart the scenario, RHA should now find the majority of the data already exists in the new datastore. Now you should be able to delete the old VMDK files if you want to.