QNAP | NAS | DUAL-CONTROLLER SERIES | MEMORY UPGRADES
ECC memory for QNAP dual-controller NAS — the ES1686dc and ES2486dc Enterprise ZFS systems, plus the TS-h2490FU all-flash platform.
Dual-controller units run two active controllers against shared storage so that a controller failure doesn't take the array offline. That architecture makes two demands on memory. Both controllers must be populated identically — same density, same rank, same speed — because a mismatch prevents failover from working, which defeats the reason you bought the system. And ZFS wants RAM: QuTS hero uses it for the ARC read cache and for deduplication tables, so memory is what determines how the array actually performs under load.
All modules here are registered ECC RDIMM in DDR4-2666 and DDR4-3200, from 8GB to 64GB, matched to QNAP's own part numbers. Order in matched pairs — one set per controller.
Not sure how many modules your configuration takes per controller? Send us the model and we'll spec it. Lifetime warranty on every module. Purchase orders, net terms and volume pricing for business, government and education buyers.
See also QNAP All-Flash NAS Memory and the full QNAP NAS Memory Cross-Reference.
The units on this page
| Model | Architecture | Per controller / socket | Slots | Memory | Documented max |
|---|---|---|---|---|---|
| ES1686dc | Dual active controllers, QES (ZFS) | Xeon D-2123IT · 32GB or 64GB shipped | 4 per controller (8 total) | DDR4-2666 ECC RDIMM | 128GB per controller |
| ES2486dc | Dual active controllers, QES (ZFS) | Xeon D-2142IT · 96GB shipped | 6 per controller (12 total) | DDR4-2666 ECC RDIMM | 128GB per controller |
| TS-h2490FU | Single controller, dual socket, QuTS hero (ZFS) | Dual EPYC 7302 / 7402 · 128GB or 256GB shipped | 8 per socket (16 total) | DDR4-3200 ECC RDIMM | 1TB (16×64GB) |
The ES units are the dual-controller systems; the TS-h2490FU is on this page because it carries the same rule in a different form — two processors that must be populated identically. Shipped configurations vary by SKU; the figures are QNAP's published ones.
Why the two sides must match, and what "match" means
On the ES units, each controller owns its pools and runs its own ZFS instance, and the partner controller holds a mirror of its state so it can take the pools over within seconds if the first fails. QES only allows a takeover between controllers whose memory configuration is identical — the standby has to be able to hold exactly what the active side held. "Identical" is stricter than "same capacity": it is the same number of modules, the same capacity per module, the same rank, the same speed, in the same slot positions on both controllers. Two controllers at 64GB, one as 4×16GB and one as 2×32GB, do not match. QES will report a memory configuration mismatch and failover is blocked until they do.
On the TS-h2490FU the reason is different but the rule is the same: EPYC memory is local to each socket, and an unbalanced layout leaves one processor reaching across to the other's memory for everything, which QuTS hero notices as a large, inconsistent drop in throughput. Populate both sockets identically.
Sizing per controller
Each ES controller serves its own pools, so size memory per controller for the pools that controller owns in normal operation — and then remember that in a failover it must hold both. QNAP's practical minimum for QES is the shipped configuration; the reasons to go past it are the same as on any ZFS system: roughly 1GB of RAM per TB of pool for an effective ARC, 1GB to 5GB per TB of deduplicated data for the dedup table, and buffer memory for busy iSCSI and Fibre Channel targets. A pair of controllers each owning 100TB with dedup on wants the full 128GB per side; a pair serving 40TB of undeduplicated file shares is comfortable at 64GB. The TS-h2490FU sizes the same way against its single pool set, with the answer split evenly across the two sockets.
Population rules
- RDIMM only. All three units are registered-memory platforms; the EC + -RD part is the whole spec. LRDIMM is not listed for these units and does not mix with RDIMM.
- Fill channels first, on both sides. Xeon D-2100 has 4 memory channels — the ES1686dc's 4 slots are one per channel; the ES2486dc's 6 slots are 4 channels with two of them doubled. EPYC 7002 has 8 channels per socket — the TS-h2490FU's 16 slots are one per channel per socket. A partial upgrade that leaves channels empty costs bandwidth on every controller or socket it is applied to.
- Buy in sets of two. Every module count you arrive at for one controller is doubled for the pair. A "4×32GB upgrade" on an ES1686dc is eight 32GB modules. The sets on this page are sized that way.
- Match rank as well as capacity. A 32GB 2Rx4 and a 32GB 2Rx8 are different modules to the controller. QES compares rank across controllers; mixed ranks in one channel on the TS-h2490FU can force a lower speed.
- The CPU sets the speed. Xeon D-2123IT and D-2142IT run DDR4 at 2400; a 2666 module is what QNAP qualified and runs at 2400. EPYC 7002 runs 3200. Buy the speed QNAP lists for the unit.
Upgrading a dual-controller unit without taking the array offline
The ES units are built to be serviced live, one controller at a time, and QNAP's hardware manual documents the sequence. In outline: from QES, fail the pools over so controller A owns everything; verify controller B is standby with no pools; shut down and remove controller B; install its full memory set; reinsert and let it boot and rejoin, and confirm QES shows it healthy and its memory reported correctly; then fail everything over to B and repeat on A. Finish both sides in the same maintenance window — until both controllers match again, failover is unavailable, which is the one state a dual-controller system is not supposed to be in. Have both sets on hand before you start. The TS-h2490FU is a single-controller unit; its upgrade is a normal shutdown.
How to check what is installed
- QES → System Status → Hardware Information shows each controller's installed capacity, slot population, module speed, and rank, side by side. On the TS-h2490FU, QuTS hero → Control Panel → System Status → Hardware Information shows the same per socket.
- QNAP's compatibility list for the model lists the RAM- parts, slots per controller, and documented maximum.
- The module label carries capacity, speed, rank, and the ECC / registered markings.
Why a tested module here
A dual-controller array is the last place to discover a marginal module — a failure on the standby side is invisible until the day it is needed. Every NEMIX RAM module on this page is specc'd on Micron, Samsung, or SK hynix DRAM to the specification of the QNAP RDIMM it replaces and run in the platform class it is listed for before it is offered. Sets are shipped as matched pairs of controller sets so both sides receive identical modules. Lifetime replacement warranty and free US-based support on every module.
Ordering for deployments
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 model, the current per-controller configuration from QES, and the target capacity to our sales team and we return a quote for both controller sets, slot-by-slot. Volume and reseller pricing is available on request.
Frequently asked
Can I upgrade one controller now and the other next month? Not without losing failover in between. The controllers must match for QES to allow a takeover. Buy both sets and do both sides in one window.
Can I add to the shipped modules or must I replace them? You can add, if the added modules match the installed ones in capacity, rank, and speed and the same is done on both controllers. Check the installed part in QES first; if the shipped modules are a different rank from what you are adding, replace the set.
2666 or 3200 for the ES units? 2666 — that is what QNAP qualified, and the Xeon D-2100 runs it at 2400 either way. 3200 is the TS-h2490FU part.
Is the TS-h2490FU dual-controller? No — dual-socket, single controller, QuTS hero. It is here because the identical-population rule applies across its two processors the same way.
Does upgrading void the QNAP warranty? QNAP documents memory as customer-upgradeable on the ES series and publishes the procedure. Adding memory does not void the warranty; our lifetime warranty covers the modules.
NEMIX RAM can deliver any Configuration your Fleet Requires
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