Hi,
what I think you see is regards the different size is the RAID configuration.
Did you check your drives before you put them in your Syn… with any other tool?
Regards the firmware, it might be very well that when you bought them your supplier tried to get rid of some [old] stock, I would contact them and ask for explanation / exchange so they are all same firmware.
In your situation I would also triple check the idle3, tler and spinup settings, I have many RED and RE4 GP drives and you would be surprised about these settings throughout all colours WD sells.
As usual my advice is before you put new drives in any raid that you make a document with all drive information. Like serial, date, firmware and LCC and other SMART data, also the slot/position they go in for easy maintenance later.
