So I am confused; got a 4 drive Synology NAS currently running 2x 1TB HDD on SHR. Just bought some 6TB HDD.s If I pull 1 HDD and add 1x 6TB, let it rebuild. Rinse and repeat with the 2nd 1TB. Will I now have a 6TB SHR (mirror) or not? if not whats my options?