After my initial upgrade to 6GB with a 4GB Crucial memory that lasted for more than 7 months with no problems, I've gone mad and upgraded the 220+ to 18GB 
It's been about a week now and no problems so far. I've never received any warnings even during the first boot after installation, it was immediately recognized.
I've ran the memory test and it passed (took more than 6 hours to complete).
Running DSM 6.2.4-25556 and vDSM 7.0
The model is Crucial CT16G4SFD8266.

It's been about a week now and no problems so far. I've never received any warnings even during the first boot after installation, it was immediately recognized.
I've ran the memory test and it passed (took more than 6 hours to complete).
Running DSM 6.2.4-25556 and vDSM 7.0
The model is Crucial CT16G4SFD8266.