The casing for the DS218+ make upgrading the first SO-DIMM difficult, it involves taking the whole device apart and flipping the motherboard while the DS718+ and DS918+ has the first slot exposed without having to disassemble the device.
The Intel Celeron J3455 CPU (4 core) in the DS718+ and DS918+ needed a different motherboard layout due to the taller heatsink for the higher temperature, this force Synology to put the motherboard facing up allowing more air flow without a metal cage design.
Lets get to disassembling the DS218+, first empty the storage bays
Remove the 4 screws from the back of the unit.
You have to tilt the metal case to allow the motherboard to be removed from the bottom casing.
Top view of the DS218+ motherboard but mounted upside down, the CPU is located here due to the heatsink being shorter and wider than the DS718+ and DS918+ heatsink. To flip the motherboard you have to remove the motherboard from the metal casing with the 4 screws
Shows a big boast in Memory performance when installing matching modules compared to the 2GB and 8GB combination set-up I had earlier.
This 16GB combination makes it closer to the Intel Atom C2538 CPU with the same Crucial 16GB set-up, the memory performance helps push the numbers up.
DS218+ 16GB vs RS215+ 16GB Compare link
The default module in the DS218+ is:
2GB DDR3L 1866Mhz CL13 1.35V,
2*Crucial 8GB DDR3L 1600MHz CL11 1.35V CT102464BF160B
There isn’t a need to get the fastest 1866Mhz module when the performance is just as good as the Intel Atom C2538.
While Synology does not recommend in replacing their default memory, it’s best that you keep the memory module in a safe place to revert the changes. Hope you find this tutorial helpful