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hardware: settle the memory line off the board QVL The manual's "memory support is to be validated" hedge was the last hard blocker on ordering. ASRock Rack publishes a 22-row memory QVL for this board, behind an AJAX tab rather than in the manual. Dual-rank ECC UDIMM at 5600 is validated, so the flagged risk was not real. But the Kingston 48GB part the pricing research was done on is not on the list; Kingston self-certifies it, which is not board-vendor validation, and this build already chose the EPYC to get that. Take 2x 32GB Micron MTC20C2085S1EC56BD1, the only 32GB ECC part on the QVL at 5600. ~$430 against ~$990 for the 48GB tier, both at 5600, for capacity 16 cores do not need. Total drops to ~$2,680.
Co-Authored-By
Claude Opus 5 (1M context) <noreply@anthropic.com>
Author: Max Johnson <me@maxj.phd> · 2026-07-25 16:59 UTC
Signed with PGP, not checked
Commit: d98134fc69c9fa1b5f80eea1ef986a1d1044ecc0
Parent: c9e6d29
1 file changed, +58 insertions, -10 deletions
@@ -41,7 +41,7 @@
41 41 |---|---|---|---|
42 42 | CPU | **AMD EPYC 4565P** (16c/32t "Zen 5", AM5) | **$589** list | 4.30 base / 5.70 boost, 64 MB L3, 170 W, 2× DDR5-5600, 28 PCIe Gen 5 lanes. Sized for throughput: clean builds, container builds, the ISO's zstd pass. See the CPU note below for why this and not a Ryzen 9950X. **Ceiling: EPYC 4005 stops at 16 cores**, so if throughput ever binds the answer is a new machine, not a new CPU — acceptable for a declared stepping stone |
43 43 | Board | **ASRock Rack B650D4U** (base variant) | ~$420 | mATX server board. **AST2600 BMC** with IPMI 2.0, iKVM, vMedia, dedicated management LAN. Base variant chosen over -2L2T/-2L2T/BCM because **it is the only one with two M.2 slots**; see the networking note for why its 1 GbE is not a compromise |
44 - | RAM | 2× 48 GB DDR5-5600 ECC UDIMM (96 GB) | ~$550 | 1 DPC runs 5600; 2 DPC drops to 3600. Two slots stay empty on purpose. **Priced $270–$1,006 for the same part number** — never buy this line without checking, see the baseline note |
44 + | RAM | **2× 32 GB Micron MTC20C2085S1EC56BD1** (64 GB) | ~$430 | DDR5-5600 ECC UDIMM, 2Rx8. **On the board QVL**, and the only 32 GB ECC part on it at 5600. 1 DPC runs 5600; 2 DPC drops to 3600, so two slots stay empty on purpose. The 48 GB tier is QVL-reachable too (SK Hynix HMCGY8MGBEB213N) but roughly doubles the line for capacity 16 cores do not need — see the memory section |
45 45 | Storage 1 | 4 TB NVMe on **M2_1** (PCIe 5.0 ×4) | ~$300 | Raw XFS **scratch**: kv-cache overflow later, container build scratch from day one. The fast slot goes to the only thing whose point is bandwidth. Buy a Gen4 drive now while NAND is expensive; the Gen5 slot is headroom |
46 46 | Storage 2 | 2 TB NVMe on **M2_2** (PCIe 4.0 ×4) | ~$200 | **xfs root**, and not ZFS — see the note in `mm-v1-bom.md`. Root gains nothing from Gen5 |
47 47 | PSU | **1200 W Platinum, ATX 3.1 with native 12V-2x6** | ~$300 | Was 850 W, which contradicted this document's own claim that two cards are reachable: 2× 250 W passive + a 170 W CPU is ~750 W, or 88% load. 1200 W also covers one modern ~450 W card. **ATX 3.1 is deliberate**: it handles the transient spikes modern cards produce and provides 12V-2x6 natively, so no adapters when the current-gen vertical gets tested. The 500–600 W-class vertical triggers a PSU review |
@@ -49,7 +49,7 @@
49 49 | CPU cooler | AM5 tower, any height | ~$100 | Air. No lid to clear on an open frame |
50 50 | Card airflow | Per-card **test sled**: server blower + shroud, per vertical | ~$150 setup | The actual thermal instrument. See the enclosure section |
51 51 | Boot GPU | **none** | $0 | The AST2600 has its own VGA and iKVM. `mm-v1-bom.md` carried a GT 1030 only because it was unsure the BMC would suffice; the manual settles it |
52 - | **Total** | | **~$2,800** | vs ~$10,280 for the `mm-v1` host platform. Line-by-line observations, spreads and market notes: `_private/docs/hardware/bench-v1/price-baseline.md` |
52 + | **Total** | | **~$2,680** | vs ~$10,280 for the `mm-v1` host platform. Line-by-line observations, spreads and market notes: `_private/docs/hardware/bench-v1/price-baseline.md` |
53 53
54 54 Vendor manuals for the decided parts are in `_private/docs/hardware/bench-v1/`.
55 55
@@ -94,6 +94,51 @@
94 94 the datasheet, so it may not be shipping; compilation gains from doubled L3 are modest, and
95 95 X3D parts usually trade all-core clock for the cache.
96 96
97 + ## Memory: the QVL settles it, and it is not the part that was priced
98 +
99 + The manual's "Memory support is to be validated" hedge was the last hard blocker on ordering.
100 + It is answered: ASRock Rack publishes a **22-row memory QVL** for this board, pulled
101 + 2026-07-25. Local copy: `_private/docs/hardware/bench-v1/b650d4u-memory-qvl.md`.
102 +
103 + **What it says, for the two things that were actually in doubt:**
104 +
105 + - **Dual-rank ECC UDIMM at 5600 is validated.** Both of the board's 5600-grade ECC entries
106 + are 2Rx8. So the worry that "ECC UDIMM + a server board + a not-quite-Ryzen CPU" would fall
107 + outside validated territory does not survive the list. Nothing about dual-rank is the risk
108 + it was assumed to be.
109 + - **48 GB at 5600 is on the list**, so the manual's 48 GB-per-DIMM ceiling is real capacity
110 + and not just a spec-sheet maximum.
111 +
112 + **Only three ECC parts on the QVL run at 5600, and each capacity has exactly one:**
113 +
114 + | Size | Vendor | Part | Rank |
115 + |---|---|---|---|
116 + | 48 GB | SK Hynix | HMCGY8MGBEB213N | 2Rx8 |
117 + | 32 GB | Micron | MTC20C2085S1EC56BD1 | 2Rx8 |
118 + | 16 GB | Micron | MTC10C1084S1EC56BD1 | 1Rx8 |
119 +
120 + Everything else on the list is 4800 or 5200. Buying off-QVL is therefore not a small
121 + compromise here: it costs a third of the memory clock, which is the same penalty as filling
122 + all four slots.
123 +
124 + **The Kingston KSM56E46BD8KM-48HM is not on the QVL.** That is the part the $270–$1,006
125 + spread was found on, and it was the presumed buy. Kingston appears on the list exactly once
126 + in ECC, as `KSM48E40BD8KM-32HM`, which is a **4800** part. Kingston's own compatibility tool
127 + does list the 48 GB module against this board — but that is vendor self-certification, not
128 + board-vendor validation, and this file already decided that distinction in the CPU section.
129 + Having chosen the EPYC over the 9950X specifically to get validated ECC, buying an off-QVL
130 + DIMM would spend that choice for nothing.
131 +
132 + **Take 2× 32 GB Micron, not 2× 48 GB Hynix.** Both are QVL and both run 5600 at 1 DPC, so
133 + this is purely capacity against cost — roughly **$430 for 64 GB versus ~$990 for 96 GB**. The
134 + BOM already held that 64 GB is enough for 16 cores, the machine is a declared stepping stone,
135 + and memory is in an up-cycle where deferring spend is the cheaper bet. The two free DIMM
136 + slots remain the escape hatch, at the 3600 penalty.
137 +
138 + One channel note: `HMCGY8MGBEB213N` is an OEM part number, so retail carries rebrands (Axiom
139 + `AX55600E46I/48G` at ~$868) rather than the SK Hynix module itself. If the 48 GB tier is ever
140 + wanted, that gap is part of its cost.
141 +
97 142 ## Enclosure: open frame, and airflow solved at the card
98 143
99 144 The earlier draft of this file argued for a 4U rackmount because a passive card "only cools
@@ -267,7 +312,7 @@
267 312 |---|---|---|
268 313 | EPYC 4565P | ShopBLT, Provantage, NeweggBusiness, Wiredzone, CDW | Niche server SKU, so **availability is the risk, not price**. Check **tray vs boxed**: tray is OEM, ships without a cooler, and the warranty runs through the reseller |
269 314 | ASRock Rack B650D4U | NeweggBusiness, Newegg, Wiredzone, ServerSupply, Provantage | Confirm it is the **base** variant, not -2L2T or -2L2T/BCM — only the base has two M.2 slots |
270 - | DDR5 ECC UDIMM | Nemix, Memory.net, ServerSupply, Newegg, Kingston Server Premier direct | Must match the board QVL. The part most likely to be wrong if bought casually, and the manual's "memory support is to be validated" hedge applies |
315 + | DDR5 ECC UDIMM | Walmart, Amazon, Memory.net, ServerSupply, OEMPCWorld, eBay | **Buy the QVL part number and nothing else**: `MTC20C2085S1EC56BD1`. Same-part asks ran $215 to $2,270 on one day, so the channel matters more than the part does. Watch for the `...BD1R` suffix, which is the same module in a different retail pack |
271 316 | 2× NVMe | Microcenter in person, Newegg, B&H | Microcenter in-store usually wins on price and removes shipping risk |
272 317 | 1200 W ATX 3.1 PSU | Microcenter, Newegg | Seasonic PRIME/Vertex, Corsair, Super Flower. Confirm **native 12V-2x6**, not an adapter in the box |
273 318 | Open frame | Mining-frame vendors (Veddha, Kingwin), or **8020 aluminium extrusion** for a custom build | Extrusion lets the sled geometry be designed in rather than worked around |
@@ -278,9 +323,13 @@
278 323
279 324 ## Open before ordering
280 325
281 - - **Does the board QVL cover DDR5 ECC UDIMM with EPYC 4005?** The manual hedges: "Memory
282 - support is to be validated." ECC UDIMM plus a server board plus a not-quite-Ryzen CPU is
283 - exactly where QVL matters. Resolve before buying DIMMs.
326 + - ~~Does the board QVL cover DDR5 ECC UDIMM?~~ **settled 2026-07-25 by pulling the QVL** —
327 + see the memory section. Dual-rank ECC UDIMM at 5600 is validated; the part is Micron
328 + `MTC20C2085S1EC56BD1`, not the Kingston module that was priced. **Caveat: the QVL carries no
329 + CPU column**, and its weighting toward 4800 parts suggests it was built in the EPYC
330 + 4004/Ryzen 7000 era. So it validates the *board*, and "with an EPYC 4005 specifically"
331 + remains unproven until the characterization gate runs. That is a bring-up risk, not an
332 + ordering blocker.
284 333 - ~~1 GbE vs 10 GbE~~ **settled 2026-07-25 by measuring the LAN** — see the networking
285 334 section. Base board, PCIE7 left empty for a future ×4-mechanical NIC.
286 335 - **OpenBMC.** `crates/bmc-agent` says it runs on "an OpenBMC fork on Aspeed AST2600-class
@@ -289,10 +338,9 @@
289 338 IPMI/Redfish or wants a dedicated dev board. **This question is not specific to this
290 339 board — it applies to the WRX90 spec identically**, and answering it on a $400 board is
291 340 cheaper.
292 - - **48 GB ECC UDIMM availability and price.** The manual lists 48 GB as the maximum module
293 - size so the spec permits it, but ECC UDIMMs are commonly 16/32 GB. If 48 GB is scarce or
294 - badly priced, 2× 32 GB (64 GB at 5600) is honestly enough for 16 cores, and 4× 32 GB pays
295 - the 3600 penalty for capacity that a fire-and-forget CI host does not need.
341 + - ~~48 GB ECC UDIMM availability and price~~ **settled 2026-07-25** — 48 GB is real and
342 + QVL-listed, but it is an OEM part sold through rebrands at roughly double the 32 GB tier.
343 + Decision: 2× 32 GB. See the memory section.
296 344 - **Where the frame physically sits.** There is no rack, and an open frame in a living space
297 345 has different constraints than a case: dust, curiosity, and anything that can be knocked
298 346 into it. Pick the spot before buying the frame.