DS211J user here, was my first NAS. Only have a 1TB WD Red installed. Use it for Surveillance, surprisingly works pretty well with 2 cameras tied into it. Using surveillance to detect motion, which is working way better than the 2 Foscams detecting motion. Much less false motion detection. It's also used as the target syno in a syno to syno backup with my 415+. Wish there was a way to update the RAM.
Just upgraded DSM from 5.2 to 6.0 last weekend. Everything went smooth. Not surprisingly took longer to update than the 415+.