How to Install RDIMM in a Synology RackStation, FlashStation or SA Series NAS

Synology's rackmount and all-flash systems use registered memory, not the SODIMM and UDIMM found in its DiskStation line. The RackStation xs+ models, FlashStation FS series and SA series all take DDR4 ECC RDIMM, and getting the install right matters more here, because a bad module can stop a unit that carries an entire business's storage. This guide covers which RDIMM each of these Synology models takes, how to install it, and what to check if the NAS does not start. If your Synology uses SODIMM, see the Synology DDR4 ECC SODIMM install guide instead.

Which RDIMM does your Synology take?

Match your exact model, printed on the label on the unit and shown in DSM under Control Panel, Info Center, to the table. Every model links to its NEMIX listing. The speed matters: some models take DDR4-3200 and others DDR4-2666, so a FlashStation FS3410 and an FS3420 are not interchangeable even though both are RDIMM. The module numbers in the last column are the Synology modules for each model, taken from Synology's DDR4 memory module page. The slot counts and maximums for the RackStation xs+ models and the FS3420 and FS6420 come from the NEMIX listings, and the others from Synology's specifications.

Many other RackStation models, such as the RS2423+, RS2821RP+, RS3618xs and RS4021xs+, use ECC UDIMM rather than RDIMM, and the DiskStation line uses SODIMM or UDIMM, so check the type before you buy. RDIMM and UDIMM are different modules and do not fit each other's slots. The Synology memory hub page covers every Synology line, and you can search by Synology part number in the Synology part number collection.

Before you start

• Know Synology's warranty position. Synology recommends its own memory modules and states that it does not provide full product warranty or technical support if non-Synology modules are used for expansion, and that other modules can cause instability or boot failures. Its warranty also excludes damage from service performed by anyone who is not a Synology representative. Decide with that in mind, and check Synology's terms for your region. NEMIX RAM modules are researched, matched, and compatibility-tested by NEMIX RAM and are backed by a lifetime warranty on the module, and each listing is built to the module type and speed Synology specifies for the model.
• Use identical modules. Synology requires that all modules in a multi-module configuration are identical, and its hardware guides require the same capacity and frequency. Do not mix 16GB and 32GB modules, and do not mix speeds.
• Keep the original module. Store it in an anti-static bag. If the NAS does not start with the new memory, putting the original back confirms the unit is healthy and is what Synology support will ask about first.
• Back up your data and plan a maintenance window, because the unit must be fully shut down. Have a small Phillips screwdriver and a clear, soft work surface, and follow anti-static precautions.
• Power the NAS down completely. Shut it down from DSM, wait until it is off, and unplug the power cords and every other cable before you open it.

How to install RDIMM in a Synology NAS

Step 1: Note the current memory

Sign in to DSM as an administrator and open Control Panel, Info Center. Write down the Total Physical Memory. You will check the same page after the upgrade.

Step 2: Shut down and unplug

Shut the NAS down from DSM, wait until the power light goes out, then unplug every power cord and the network, USB and expansion cables. Do not change memory with the power on.

Step 3: Open the unit

Synology's hardware installation guides for these systems begin the same way. On the FS3600 and the RS3618xs, remove the screw on the back and pull off the rear top cover. Touch only the memory assembly once the cover is off. Some systems need more: Synology's FS6400 guide also has you remove the beam (four screws on each side of the chassis) and the air duct cover (three screws). Use the hardware installation guide for your exact model from Synology's downloads, or send us your model and we will tell you what we know before you open it.

Step 4: Release the old module if replacing

On a unit shipped with a module in place, Synology's FS3600 guide has you cut the cable tie that secures the pre-installed module for shipping, taking care not to touch other motherboard components. Then push the retaining clips on both sides of the slot outward and the module pops out. Hold modules by their edges and never touch the gold contacts.

Step 5: Seat the new module

Push the retaining clips outward. Line up the notch on the module's gold edge with the notch in the slot, then press down with firm, even pressure until the clips snap into position. Population order matters. On the RS3618xs, Synology says to fill the white slots first. On the FS6400, it says to install the modules in slots A0 and D0 first. On the FS3600, the four slots are labeled A0, A1, B0 and B1 and Synology lists these combinations:

Check the hardware guide for your model for its own slot layout. The module should seat without force. If it resists, check the orientation and the memory type.

Step 6: Close the unit and power on

Refit the air duct and beam if you removed them, align the markings on the side of the rear top cover with the slots on the chassis edge, push the cover into position and reinstall the screw. Reconnect the cables and power on.

Step 7: Confirm the new total in DSM

Sign in to DSM as an administrator and open Control Panel, Info Center. Total Physical Memory should show the new capacity. Leave the NAS under your normal workload for a while and check that it stays stable.

If the NAS does not start or shows less memory

1. Shut down, unplug the power cords and open the unit again.
2. Reseat each module until the clips snap into position.
3. Check that the modules are DDR4 ECC RDIMM at the speed listed for your model, that all of them are identical, and that you filled the slots in the order the hardware guide gives.
4. Try one module in the first slot. If a single module works and the set does not, one module or the configuration is the problem.
5. If the unit powers on but DSM does not load, remove the new modules and start with the original, then tell us your model and we will help with the right module.

How much memory should you install?

Synology states that volumes over 108 TB need at least 32GB of memory, and that a 1 PB volume in RAID 6 needs 64GB. Beyond that, virtualization, snapshots, deduplication and heavy random I/O on all-flash systems all benefit from more. The 4-slot systems stop at 128GB, the 6-slot RS4826xs+ and RS6426xs+ at 96GB, the FS3420 at 192GB, the FS6400 at 512GB and the 16-slot systems at 1TB. Do not exceed the maximum Synology specifies for your model.

Find your memory

• By series: RackStation memory, FlashStation memory and SA series memory.
• The Synology memory hub page and the Synology memory guide.
• By type: DDR4 ECC RDIMM.
• Other brands: NAS memory by brand.

Buying for several systems

NEMIX RAM is a US-based memory specialist, in business since 1993. Every module is researched, matched, and compatibility-tested by NEMIX RAM, is JEDEC-compliant, and is backed by a lifetime warranty. IT teams, schools and integrators that run several Synology systems can standardize on one kit per model. Purchase orders, net terms and volume pricing are available. Request a quote with your models and quantities, or contact our sales team.

NEMIX RAM is an independent memory supplier and is not affiliated with Synology. Synology, RackStation, FlashStation and DSM are trademarks of their respective owners, used only to identify compatible systems. Steps are summarized from Synology hardware installation guides for the FS3600, RS3618xs and FS6400 and from Synology product pages; follow the instructions for your exact model.