20 January 2017
The Pegasus3 unit is shipped with RAID 5 configuration, so once you connect the unit it will start the Synchronization process which will take few hours to complete and once it is done you can start moving files to the new array.
Please use the below the link to download the user manual and check Pg#89 to know more on Synchronization:
About the issue, you may not be able to mirror the Pegasus volumes, it will be mounted as seperate volumes and you can manually move files to the new array. In case if you have the both the Pegasus units (Peagsus 2 and Pegasus 3 )daisy chained then please disconnect it and connect the Pegasus 2 unit to a secondary Thunderbolt port on your mac and see if it is detected/Mounted.
Please contact Promise Tech support for any further assistance.