Parts-Quick 4GB Memory for SYNOLOGY DS918+ DDR3L SO-DIMM RAM Module at Amazon.com
A-Tech 16GB Memory RAM for Synology DS DS1621+ - DDR4 2666 PC4-21300 ECC SO-DIMM 2Rx8 1.2V - Single NAS Server Upgrade Module (Compatible Replacement for D4ECSO-2666-16G) at Amazon.com
The DS918+ NAS Supports upto 16GB Memory – An installation Guide – NAS Compares
Synology DS918+ 16GB Guide – NAS Compares
Amazon.com: Timetec Hynix IC 8GB Compatible for Synology NAS DiskStation DS218+ DS918+ DDR3/ DDR3L 1866Mhz PC3L-14900 1.35V Non-ECC Unbuffered 204 Pin SODIMM Memory RAM (8GB) : Electronics