Synology Inc. D4ES01-4G 4GB DDR4 ECC SO-DIMM memory upgrade

Synology 21-series ECC SO-DIMM

This 4 GB DDR4 module is built for Synology 21-series NAS units including the RS1221RP+, RS1221+, DS1821+ and DS1621+. It adds error-correcting memory to systems that support ECC, helping maintain data integrity during continuous operation. The unbuffered design matches the memory controller in these models.

260-pin DDR4 form factor

The stick uses the standard 260-pin SO-DIMM layout, so it slots directly into the memory socket on the compatible Synology mainboard without adapters. ECC circuitry works transparently once installed, and the unbuffered signalling keeps latency low for the workloads these appliances run. No extra configuration is required beyond seating the module firmly.

Upgrade from non-ECC or lower capacity

Owners of the listed 21-series units who currently run non-ECC memory or a single smaller module can install this kit to gain error correction and additional headroom. The jump is worthwhile when the NAS handles critical file services, virtualization or backup tasks where silent data corruption is unacceptable. Systems not in the 21-series compatibility list cannot use this module.