SYNOLOGY | DISKSTATION | RACKSTATION | FLASHSTATION | SA-SERIES | UC-SERIES | NAS DEVICE | OEM SKU | COMPATIBLE MEMORY | CROSS-REFERENCE
Memory matched to Synology OEM Part Numbers — for DiskStation, RackStation, FlashStation and SA-Series, UC-Series NAS Devices.
All Synology Part Numbers Cross-Referenced across all models, all DDR4 at 2133MHz through 2666MHz, from 4GB to 64GB. Synology's codes tell you exactly what a unit takes:
D4ER01ECC registered RDIMM — FS3410, SA3410, SA3610, SA6400, HD6500D4RDECC registered DIMM — RackStation xs+ unitsD4EC/D4EU01ECC UDIMM — RS2423+, FS2500D4ES01/D4ES02/D4ECSOECC SODIMM — RS822+, DS3622xs+, DS2422+D4NE/D4NESO/D4NSnon-ECC — DS224+, DS1618+, DS1819+, DS2419+
Those prefixes are not interchangeable. A unit specified for D4ER01 registered memory will not post with the D4EC unbuffered part, even at the same capacity and speed — and Synology reuses similar capacity suffixes across all of them, which is where orders go wrong.
One thing to know before you buy. Synology's DSM may flag non-Synology-branded memory as unverified on some models, and Synology's warranty position is that only its own modules are supported. Every module here is built to the same specification as the part it references, but if your deployment has a support contract that hinges on OEM parts, that's a decision worth making deliberately rather than discovering later.
Use Shop by System Model to filter to your unit, or send us the model and we'll confirm the part, the slot count and the maximum. Lifetime Replacement Warranty on every module. Purchase orders, net terms and volume pricing for business, government and education buyers.
Model by model: slots, factory module, documented maximum
The prefixes above tell you the type; this tells you the count and the ceiling. Figures are Synology's published ones; the model's specification page on Synology's site is the authority for any unit not listed.
| Family | Models | Processor | Factory | Slots | Max | Synology part |
|---|---|---|---|---|---|---|
| Plus 2025 | DS725+, DS925+, DS1525+, DS1825+ | Ryzen V1780B | 4GB / 8GB | 2 | 32GB | D4ES02-4G · D4ES02-8G · D4ES01-16G (ECC SODIMM) |
| Plus 2022 – 2023 | DS723+, DS923+, DS1522+ | Ryzen R1600 | 4GB / 8GB | 2 | 32GB | D4ES02-4G · D4ES02-8G · D4ES01-16G (ECC SODIMM) |
| Plus 2020 – 2021 | DS1621+, DS1821+, DS2422+ | Ryzen V1500B | 4GB | 2 | 32GB | D4ECSO-2666-4G · -8G · -16G (ECC SODIMM) |
| Value Plus (Celeron J4125) | DS224+, DS423+, DS920+, DS720+, DS420+ | Celeron J4125 | 2GB or 4GB soldered | 1 open | 6GB or 8GB | D4NESO-2666-4G (non-ECC SODIMM) |
| Value Plus (Celeron J3455) | DS918+, DS718+, DS418play | Celeron J3455 | 2GB or 4GB soldered | 1 open | 6GB or 8GB | D3NS1866L-4G (DDR3L non-ECC SODIMM) |
| xs+ tower | DS1621xs+, DS3622xs+ | Xeon D-1527 / D-1531 | 8GB / 16GB | 2 | 32GB / 48GB | D4ECSO-2666-8G · -16G (ECC SODIMM) |
| Atom C3538 tower | DS1618+, DS1819+, DS2419+ | Atom C3538 | 4GB | 2 | 32GB | D4EC-2666-4G · -8G · -16G (ECC UDIMM) |
| RackStation Plus | RS822+, RS1221+, RS2421+, RS2821RP+ | Ryzen V1500B | 2GB / 4GB | 2 | 32GB | D4ES01-4G · -8G · -16G / D4ECSO-2666 (ECC SODIMM) |
| RackStation Plus 2023 | RS2423+, RS2423RP+ | Ryzen V1780B | 8GB | 2 | 32GB | D4EU01-8G · -16G (ECC UDIMM) |
| RackStation xs / xs+ (current) | RS1619xs+, RS3618xs, RS3621xs+, RS3621RPxs, RS4021xs+ | Xeon D-1527 / D-1521 / D-1541 | 8GB / 16GB | 4 | 64GB | D4EC-2666-8G · -16G / D4EC-2400 (ECC UDIMM) |
| RackStation xs+ 2017 | RS3617xs+, RS4017xs+, RS18017xs+, FS3017 | Xeon D-1531 / D-1541 | 8GB / 16GB | 4 – 8 | 64GB / 128GB | D4RD-2400-8G · -16G (ECC RDIMM) |
| FlashStation | FS2500 · FS3410, FS3600 | Ryzen V1780B · Xeon D-1541 / D-1567 | 8GB · 16GB | 2 · 4 | 32GB · 128GB | D4EU01 (ECC UDIMM) · D4ER01-16G / -32G (ECC RDIMM) |
| SA series | SA3410, SA3610 · SA6400 | Xeon D-1541 / D-1567 · EPYC 7272 | 16GB · 32GB | 4 · 8 | 128GB · 512GB | D4ER01-16G / -32G (ECC RDIMM) |
| HD series | HD6500 | EPYC 7272 | 64GB | 8 | 512GB | D4ER01-32G (ECC RDIMM) |
| UC series (dual controller) | UC3200, UC3400 | Xeon D-1521 per controller | 8GB per controller | 2 per controller | 64GB per controller | D4RD-2666 / D4ER01 (ECC RDIMM) — identical on both controllers |
Two families do not appear because they cannot be upgraded: the j and Value lines (DS223j, DS224, DS423, DS124, DS223, DS923-class without the plus) are ARM or soldered-only, and the DS2xx / DS4xx non-plus Intel units solder their memory. If DSM's Info Center shows memory but the specification page shows no memory slot, the unit is one of these.
Reading the code, one field at a time
D4 ES 02 -8G | | | | | | | └─ capacity | | └────── revision (01, 02, 03 — same spec, different qualified DRAM) | └─────────── type: ER = ECC RDIMM · RD = ECC RDIMM (2400 era) · EC / EU = ECC UDIMM | ES / ECSO = ECC SODIMM · NE / NESO / NS = non-ECC SODIMM └──────────────── generation: D4 = DDR4 · D3 = DDR3 / DDR3L
Older parts carry the speed in the middle — D4ECSO-2666-16G, D4EC-2400-8G, D3NS1866L-4G — and the newer ones move it into a revision number, so D4ES01 and D4ES02 are both DDR4-2666 ECC SODIMM and differ only in which DRAM Synology qualified. They are interchangeable within a unit; the NEMIX RAM module listed against either is built to the common specification. The one place the intro's "all DDR4" needs a footnote is the J3455 generation and older, which is DDR3L at 1.35V — the D3 prefix — and does not accept a DDR4 module or a 1.5V DDR3 one.
Population by unit type
- Soldered plus one slot (J4125 and J3455 units): the slot takes one module and the soldered 2GB or 4GB stays. Synology documents 4GB in the slot; 8GB and 16GB modules are widely reported to work in the J4125 units and are outside the documented configuration. Whichever you choose, it is a single module — there is no pairing decision.
- Two slots (Plus, RackStation Plus, xs+ tower): two identical modules for dual-channel. Replacing the factory 4GB with a matched pair of 8GB or 16GB is the clean upgrade; adding one 16GB to the factory 4GB runs at 20GB with the mismatch costing speed on the Ryzen units.
- Four-slot UDIMM units (RackStation xs / xs+): populate in pairs per Synology's slot order; four identical for 64GB.
- RDIMM units (FS, SA, HD, 2017 xs+): fill every channel before doubling — 4 per socket on Xeon D, 8 on the EPYC units — in the order the hardware guide shows.
- UC dual-controller units: identical modules in identical slots on both controllers, installed in the same maintenance window; DSM UC will not fail over between mismatched controllers.
- The CPU sets the speed. Every current unit is DDR4-2666 or runs a 2666 module at 2400 (Xeon D-15xx, Atom C3538). A 3200 module fits and runs at the unit's speed; buy 2666.
How much memory a Synology actually uses
DSM itself is comfortable at 2GB. Everything above that is the packages: Btrfs keeps metadata and checksums resident and gets faster with headroom; Container Manager and Virtual Machine Manager take whatever the containers and guests are allocated, and VMM will refuse to start a guest the host cannot back; Synology Photos and Plex index and transcode in memory; Active Backup for Business deduplication holds its hash table in RAM and is the single largest consumer on a backup unit; Surveillance Station scales with camera count; SSD cache reserves memory proportional to cache size, and DSM will not let you create a cache the memory cannot support. A DS923+ at its factory 4GB running Photos, a couple of containers, and an SSD cache is at its limit; 16GB or 32GB is what makes the same unit feel like a different machine. On the SA and FS units running iSCSI to a hypervisor, the same rule as any ZFS-class system applies: more memory is more cache, and the array is faster for it.
What DSM shows, and what it does not
- Control Panel → Info Center → General shows total physical memory. On DSM 7.2 and later, Info Center → Hardware & Power or the memory line lists slot population on units with slots.
- The notification the intro describes — a non-Synology module installed — appears in Notification Center and on Info Center once, at boot, on some models. It does not block a package, a volume, or an update, and the full capacity is reported and used. It is a label, not an error.
- The module label under the drive tray or the side panel carries the D4 code.
- Synology's specification page for the model states the factory module, slot count, maximum, and the current part number for expansion.
The 2025 drive policy does not extend to memory
Synology's 2025 Plus models restrict full functionality to Synology-listed drives. Memory is not part of that policy — DSM on the DS925+, DS1525+, and DS1825+ treats third-party memory the same way earlier units do: the informational notice on some, full capacity recognized and used on all. Our modules for those units are built to the D4ES02 specification and run in them before they are offered.
Why NEMIX RAM for Synology
Every module we list for a Synology is detailed to Micron, Samsung, or SK hynix DRAM to the specification of the D-series part it replaces — ECC where the part is ECC, registered where the unit is registered, 1.35V where the unit is DDR3L, the same rank and organization — and run in the unit family it is listed for before it is offered. Lifetime replacement warranty and free US-based support on every module; if the unit ever has a memory question, we are the ones who answer it.
Ordering for a deployment
Synology units are bought by the office, the branch, and the rack. NEMIX RAM is a registered federal supplier (UEI GV8MMYNDJ5J1, CAGE 59AB2) and accepts purchase orders with net terms for business, government, and education buyers. Send the models, unit count, and target capacity per unit to our sales team and we return one quote with a matched set per unit, controller pairs called out on the UC units. Volume and reseller pricing is available on request.
Frequently asked
D4ES01 or D4ES02 for my DS923+? Either; same specification, different qualified DRAM. Synology ships D4ES02 in the current units and lists D4ES01-16G as the 16GB part for both.
Can I put 32GB in a DS923+ that ships with 4GB? Yes — two 16GB ECC SODIMMs, and Synology documents 32GB as the maximum. Remove the factory 4GB.
Will 16GB work in a DS224+ or DS920+? Widely reported to, and outside Synology's documented 6GB / 8GB. The J4125 controller is rated for 8GB total; it is your call, and the 4GB module is the supported one.
Do I need ECC on a DS923+? Synology specifies it; the unit's controller runs it; Btrfs checksumming and ECC are the two halves of the data-integrity case the Plus line is sold on. Buy the ECC part.
Will the DSM notice go away? On the models that show it, it appears once per boot in Notification Center and can be dismissed. It does not recur during operation and does not affect the unit.
Does upgrading void the Synology warranty? Synology documents memory as user-installable on every unit in the table. The hardware warranty on the NAS stands; Synology may decline to troubleshoot a fault it attributes to third-party memory, which is what our lifetime warranty and support are for.
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