Why not go with RAID5? It gives you 6TB space.
I am running an old DS406e on DSM 3.1 firmware 1635. All successive upgrades untill this point went smooth. A few days ago I tried to upgrade to the firmware 1955, which ended up in an error message, basically saying that the file would be corrupted.
@megagega - I'm guessing I did something wrong then. I currently don't have time to take a look at it, and will probably forget afterwards... Yeah, I'm terrible at this, sorry.
You do realise the HDD leds aren't functioning, right?