San clemente also has a weakness. Dual channel memory vs quad channel on Harpertown. On DB workloads, you can see quiet a bit of difference. On single threaded apps, they can’t use the quad channel fully. Also, FB-DIMM gives you protection on the address lines as well as data compared to only data on the registered DIMMs.

16GB or 32GB of ram is last year’s hardware. Right now, Dell R900 with 128GB is a potent DB platform. Within a year, when DDR3 market settles down(ie. Price parity per GB compared to DDR2), hopefully the Nehalem platform is mature too then, with possibly a shrink to 32nm Sandy Bridge. Then is the time to buy Nehalem. It is kind of stupid to only give 2S Nehalem 24GB of ram(12x 2GB) for a server considering the awesome bandwidth.

Fit everything in ram. Max the ram sockets. Then max the hot swappable SAS bays with SSDs. That’s the way to do it nowadays. You are dead if you have to seek on rotational hard drive. Those are web 2.0 ways.

Yes you’re right that San Clemente only supports 6 dual-rank DIMMs (officially from Intel). Tyan however will certify and support 8 dual-rank DIMMs which for most people is enough. If you need more RAM and you’re not willing to wait for Nehalem-EP, then Harpertown with FBDIMM or Shanghai with DDR2 unbuffered are your only options, and Shanghai comes out with better performance/power. If you need less than 24 or 32 GB of RAM, San Clemente and Harpertown are your best deal.

AMD had lost power advantage since the Harpertowns came out. To compensate, the AMD realized that its memory controller has room to fudge numbers. The memory controller on the Opterons can control up to 16 ranks of memory per Socket. For a 2S system, you could load up to 16 DIMMs of Dual rank memory. However, you don’t have to fully load up the memory ranks. You can easily load 2 single ranks on each processor, effectively using only 4 ranks total vs 32 total ranks that’s supported. That gives you the 20W difference between AMD’s ACP(75W) and AMD’s TDP(95W)

I think that comparing a Nforce 3600 chipset based Shanghai system to a 5100 Intel San Clemente is unfair for AMD because the Intel system only gives you 12 ranks of total memory. (when 12 ranks are used, 5100 converts into 48GB mode and uses a little more power than if 8 ranks are used in normal mode) Most san clemente systems on the spec2008 power benchmark site use 4 dimms of dual rank 4GB ram to minimize power usage(by the way, those are 2Gbit chips, so power is lower too compared to 1Gbit chips)

All in all, I think the L5410, L5420s on San clemente is a very potent web frontend box, and AMD Shanghai’s are pretty good backend database boxes, or memcache boxes. Although with the release of Dell R900 bios v1.1.9, the 7300 intel chipset now supports a whooping 128 total ranks of memory, giving you a 32 dimm*8GB quad ranks= 256GB total for very little money. I would now claim here that even with the disadvantage for FB-DIMMs, the R900 is the best Database box money can buy right now(4GB Quad rank memory is too cheap to ignore. Paying 2200 dollars for 32 dimms of 4GB quad ranks is too good, that Oracle and MySQL people would now have access to 128GB machines for less than 5000 dollars.

- AMD claims that Intel’s current chipsets consumes more power than AMD-based chipsets.
- AMD claims that Intel’s 80W-TDP CPU consumes more power than AMD’s 75W-ACP CPUs.

Yet when it’s all said and done, Intel’s overall system power consumption is lower than AMD despite having a CPU rated at higher power and despite having a chipset rated at higher power.

Since it’s an accepted fact that Intel’s current chipsets (which include a memory controller) do consume more power than AMD chipsets, the only thing that explains this system-level power discrepancy is that AMD’s CPU power rating "ACP" is grossly inflated.