Niall’s virtual diary archives – Saturday 24 August 2019

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Saturday 24 August 2019: 00:17. Spent this Friday evening implementing tags support for this website, such that say #meetingcpp would now list all posts which tagged #meetingcpp. You can even see a list of all tags, where you will find much evidence of the automated conversion script which generated this Hugo website from the original website.

I don’t have a huge amount to report, really. Tipping away at work, making hay before the next recession bites, which is very soon now, only the US is not in recession, and it’ll tip soon now as well making a global universal economic recession. So best to husband ones resources in my book, though I expect this to be a mild recession. I did have to buy this week an unholy 128Gb of RAM for my Threadripper workstation for work reasons. When I bought it last May, I fitted it out with 32Gb which seemed reasonable at the time. And it would have been, but a work project sucks down 20Gb of RAM, and under the ThreadSanitiser that explodes to about 80Gb. So, I must buy 128Gb, which is an insane amount of RAM.

AMD Threadripper v1 and v2 didn’t get anything like the RAM compatibility testing which Intel HEDT gets, so finding 8x 16Gb RAM sticks which are known compatible with Threadripper was very hard. Or, rather, you could find quite a few underclocked 128Gb RAM configurations on the motherboard vendor QVL lists, but very little information on which specific RAM stick model numbers would work at high speed in an 8x configuration. Almost nobody fits 128Gb RAM to Threadripper in other words, or rather, very few of those who do do not post what works onto the internet.

Given the cost of 128Gb of RAM (approx €600-€1000 ex VAT, depending on speed and CAS latency), even in these days of super-low RAM prices, I had no choice but to take a shot in the dark. After a very great deal of weighing of options over two weeks of research, I ended up plumping for 8x M391A2K43BB1-CTD Samsung 16GB DDR4-2666 ECC UDIMM PC4-21300V-E Dual Rank x8 Module sticks. Motivating factors were:

  1. Samsung memory sticks (Threadripper is known to particularly like Samsung memory)
  2. ECC memory sticks (so I can tell what is a reliable overclock)
  3. Cheaper than the alternatives

The fastest I could find on any QVL list for full x8 stick occupancy for the AMD X399 chipset was HX430C15PB3K8/128 Kingston HyperX 128 GB (Kit 8 x 16 GB), 3000 MHz CL15 DIMM XMP, made from Hynix RAM chips. This is on the QVL list for a Gigabyte X399 chipset motherboard, same chipset as mine, but not mine. And not ECC RAM. Best price I could find was €647 ex VAT.

Best single online user report of full x8 stick occupancy compatibility that I could find was F4-3200C15Q2-128GTZ G.SKILL TridentZ Series 128GB (8 x 16GB) 288-Pin DDR4 SDRAM DDR4 3200 (PC4 25600), supposedly made from Samsung B-die chips. Not ECC RAM. Best price I could find was €779 ex VAT.

Contrast those to the Samsung M391A2K43BB1-CTD, 8x of which I found for €564 ex VAT. This is theoretically way slower RAM, 2666 @ CAS 19 is 14.25ns, whereas the Kingston will do 3000 @ CAS 15 = 10ns. But the four – yes just four – online user reports of using Samsung ECC RAM with Threadripper which I could find suggest that it overclocks very well. The native 2933 of Threadripper v2 @ CAS 15 is apparently easily achievable with Samsung ECC RAM rated for 2133, just force an overclock. I thus hope that my considerably more modern 2666 Samsung ECC RAM will make 3200, and if not, 2933.

(The 3200 is because Threadripper v2 shows an excellent performance improvement up to 3200, but not so much thereafter. AMD chose 2933 over 3200 because of idle power consumption rather than sweet spot performance, it’s about a quarter worse in idle power)

I’ve had my Threadripper workstation for about five months now. I really must recommend it, if you can afford it. It’s been utterly rock stable, much more so than the Intel system which preceded it, or even the Intel one before that. In fact, it’s as rock stable as my last AMD system, which was a server-grade dual-Athlon workstation which I had 2001-2007, which apart from its hideous idle power consumption of 270w (??? my memory may be faulty?), was a great computer. And why I kept using it so long. Threadripper superlative stability isn’t that surprising, Threadripper is really an EPYC server-grade CPU, just with half its memory channels disabled, so you get that server-grade reliability from all the conformance and reliability testing which they do for server, but not consumer, hardware.

Indeed, such has been the solidity of my existing Threadripper system without ECC RAM, that I would wonder what benefit ECC RAM would actually bring? Sure, I understand the statistics, but the probability of a random cosmic ray bit flip affecting anything important are vanishingly small in 128Gb of RAM! Anyway, let’s hope that the new RAM POSTs at all. It should arrive early September,




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