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AMD sent us a Titanite SP5 reference platform for our tests. This is a reference platform, so not all of its specs are necessarily POR — refer to AMD’s official specifications for any needed clarifications.
As you can see, the system is a standard 19” 2U rack server that can accommodate two Genoa processors up to 400W. The system has 24 DDR5 slots populated, though the company actually routed 28 slots for 2DPC developmental purposes. The system has four x16 xGMI links, with one cabled link enabling 3L or 4L configurations.
The system has dual 2000W redundant power supplies, though it dynamically spreads the power load across both power supplies during use. As such, we were advised to plug the system into two separate circuits, as the peak power consumption can trip a single circuit breaker. The remainder of the slides are self-explanatory and show the system’s accommodations quite well, so we won’t bother repeating them.
The system has twenty-four 2.5” NVMe bays up front, leveraging EPYC’s incredible PCIe connectivity, but we used the in-built M.2 port for our tests. As you can see, the system has a large black air baffle directing air over incredibly large heatsinks with a large frontal fin stack — more on those in a second.
We can also see six fans aligned across the front of the system. These 20,000-RPM fans alone can draw up to 300W when the system is under full load. That’s necessary to cool the 800W of CPU power, and the additional ~300W of power used by just the 1.5TB of DDR5 memory.
As a result of such high secondary power consumption, power measurements taken at the wall plug aren’t effective for precise measurement. We’re working on exposing software-based counters to quantify power consumption for this review, but that is a work in progress.
We did see ~1800W of power use at the wall for the system during heavy workloads like Gromacs and OpenSSL, but again, a big portion of that power consumption is due to the fans and memory, so it will vary widely based upon the system and memory configuration. Notably, the 2000W power supplies are 80 Plus Titanium rated and incredibly small given their output.
The motherboard houses multiple rows of VRMs, all dedicated to delivering power to the socket. (Remember, DDR5 has the power circuitry on the DIMM itself.) Two rows of these VRMs are arranged in a ‘flying V’-esque formation to avoid the various motherboard traces on one side and the DDR5 DIMMs on the other. Board space is obviously at a premium.
We also see several cables that plug into the motherboard near the CPU sockets. These connections are splayed across the motherboard in a seemingly haphazard fashion, but this is to prevent wiring crossovers that would prevent such a dense cabling arrangement. You’ll see similar designs in shipping servers to provide enough cord clearance.
These cables carry the I/O interfaces to the server's front panel, but that requires rather complex routing. This complex routing could be eased by using one of the two cabled Infinity Fabric links between the fans and the DRAM slots in the center of the chassis. Interestingly, AMD chose not to use a 3L implementation in this reference platform, but this cabling is a perfect example of why it is so useful.
The system has 12 DRAM slots flanking each socket, for a total of 24. As you can see in the image of the DDR5 sticks, there are solder pads for one additional DRAM slot per side, but AMD chose not to mount them for this platform. Instead, these will be used to qualify 2DPC arrangements.
Interestingly, DDR5 slots are soldered directly to the top of the motherboard as a surface mounted device (SMD), whereas DDR4 slots are soldered through the board entirely. This SMD mounting is needed to accommodate the tighter signal integrity requirements of DDR5, but it does result in much 'weaker' slot attachments. Additionally, AMD has to use skinnier DDR5 slots to cram 12 channels of memory into a standard 2U server chassis.
AMD cautioned us that it has had several incidents where any lateral pressure when installing the DDR5 DIMMs can strip the DIMM socket off the board due to this weaker connection. We were also told to use caution when installing the heatsinks to avoid jostling the DDR5 slots due to their fragility.
The heatsinks are massive affairs that consume far more space than we’re accustomed to seeing with previous-gen systems. As you can see, the rear of the assembly is what we would consider a ‘standard’ server CPU air cooler, much like the ones you’ll find on any AMD or Intel system. The copper cooling core mates with the CPU in standard fashion, but AMD elongated Genoa’s IHS specifically to provide more surface area to dissipate heat into the sink.
The standard portion of the heatsink has heatpipes that carry excess heat to the forward fin stack — a not-so-new but relatively rare innovation that will now become much more standard in air-cooled servers. This forward area has two fin stacks sandwiching the heat pipes, all of which provide previously unmatched cooling capabilities.
This (for lack of a better term) ‘dual-stage’ type of air cooler is largely responsible for enabling the higher level of power consumption, and thus performance, in air-cooled servers. Combined with smart system engineering to ensure tightly directed airflow over both the forward and rear fins stacks (helped along by the black air baffle), these heatsinks can dissipate up to 400W of thermal load. However, it isn’t clear if this type of heatsink will only be used in the highest-power servers, or if we’ll see these on lower-end servers as well. The fans are all hot-swappable, with power connectors integrated directly into the motherboard.
The SP5 socket is a beast of an LGA affair, housing 6,096 pins in a 72 x 75.4mm footprint and satisfying up to 400W processor TDPs.
The chip installation process will be familiar to anyone who has used AMD’s SP3 socket. However, the socket relies upon hold-down pressure from the six-fastener heatsink rather than the three screws we’re accustomed to with the SP3 socket.
Instead, one screw holds the chip down in the latching mechanism, while tightening the heatsink screws in a star pattern provides the hold-down pressure for firm mating. We found that this mounting technique is far superior to SP3 in ensuring good contact between the chip and the pins. It certainly isn’t uncommon to have memory channels disappear due to poor contact after changing chips in an SP3 socket, but we didn’t have those issues with the new SP5 mechanism after multiple chip swaps.
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