Memory 32 g for Synology DiskStation DS1821+ 8-Bay NAS Enclosure, 4-Core 2.2 GHz, 4 GB RAM, No HDD

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Yes, you will need to look for RAM 32GB 260-Pin DDR4-2666 PC4-21300 ECC Sodimm Dual Rank 2Rx8 1.2 volts 2666MHz. https://amzn.to/3QzJk04
There is also alternative RAM mentioned here https://nascompares.com/answer/ds1621and...ch-memory/
And the rest here https://nascompares.com/2021/04/28/synol...lkthrough/

Compatible 10GbE cards:
Synology E10G18-T1 1 x 10GbE RJ45 PCIe 3.0 x4
Synology E10G18-T2 2 x 10GbE RJ45 PCIe 3.0 x8
Synology E10G21-F2 2 x 10GbE SFP+ PCIe 3.0 x8
Synology E25G21-F2 2 x 25GbE SFP28 PCIe 3.0 x8
Intel Ethernet Converged Network Adapter X710-T4 X710-T4 5.05 4 x 10GbE RJ45 PCIe 3.0 x8
Marvell FastLinQ QL41134HLRJ QL41134HLRJ 8.34.15 4 x 10GbE RJ45 PCIe 3.0 x8
Synology (EOL) E10G17-F2 2 x 10GbE SFP+ PCIe 3.0 x8