LRDIMMs, RDIMMs, and Supermicro's Latest Twin
by Johan De Gelas on August 3, 2012 4:45 AM EST- Posted in
- IT Computing
- Intel
- Samsung
- Xeon
- Cloud Computing
- Supermicro
Low Level Measurements
Before we start with the rather complex virtualization benchmarks, it is good to perform a few low level benchmarks. First, we measured the bandwidth in Linux with our Pathscale compiled Stream binary on the latest Ubuntu Linux. For more details about our Stream binary, check here.
To get a better understanding we tested the 8GB RDIMMs at both the rated speed (1600MHz) as well as configured (via the BIOS) as 1333MHz DIMMs. The comparison of 1333MHz RDIMM and LRDIMM allows us to measure the impact of the iMB buffer. That impact is small but measurable: RDIMMs offer about 5% more bandwidth than LRDIMMs at the same speed. 1600MHz RDIMMs offer 14% higher bandwidth than LRDIMMs.
Of course, bandwidth only matters when you run out of it. Latency always matters, although a 15MB (up to 20MB) L3 cache can hide a lot of memory latency. We tested memory latency with AIDA64.
The iMB adds about 11% if we disable turbo and compare the LRDIMM and RDIMM at the same clockspeed (1333MHz). Somewhat interesting is that the latency of the RDIMM at 1600MHz is higher. The memory chips are accessed with a significantly higher CAS and RAS to CAS latency at 1600MHz, which explains this counter intuitive result. Once we enable turbo, the latency differences get very small. The iMB causes only 2% extra latency, which is negligible.
The conclusion so far: the iMB decreases bandwidth by a measureable but small amount, but the latency impact is hardly measurable.
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ddr3memory - Monday, August 6, 2012 - link
Your article is very interesting - and the first mainstream (and belated) examination of the LRDIMM (new standard - incompatible with RDIMMs) vs. HCDIMM (100% DDR3 RDIMM compatbile) choice for Romley.I have whittled down the use case for HCDIMMs/LRDIMMs and RDIMMs as follows:
The HCDIMM use case is at:
- 16GB at 3 DPC use
- 32GB (outperform both RDIMMs and LRDIMMs)
LRDIMMs are not viable at:
- 16GB (RDIMMs are better)
- 32GB (HCDIMMs are better)
RDIMMs are not viable at:
- 32GB (because they are 4-rank - trumped by LRDIMMs/HCDIMMs)
There is a reason the Netlist HCDIMMs were only released on the virtualization servers from IBM/HP - because at 16GB levels the only niche available for LRDIMM/HCDIMM vs. RDIMM is the 3 DPC space. This will expand considerably at 32GB to mainstream levels as soon as 32GB HCDIMMs are released (they are currently in qualification with IBM/HP and have not been announced yet - though maybe expected shortly).
I had created an infographic covering the memory choices - search the net for the article entitled:
Infographic - memory buying guide for Romley 2-socket servers
HCDIMMs are not available at SuperMicro (as they are for IBM/HP) - so I was surprised you even covered HCDIMMs (since the article is after all referring to the SuperMicro line of servers).
Casper42 - Friday, August 10, 2012 - link
BTW, Johan, I work for HP and asked some of the guys in ISS Technical Marketing why we don't send you our servers for eval like you get from SuperMicro and sometimes DellThey felt that you guys didn't do alot of Server Reviews, and that your readership wasn't generally the kind of folks that buy HP Servers.
So I am curious if you could spin up a poll or something in the future to prove them wrong.
If there is enough support I'm sure we can you some gear to play with.
I sometimes giggle when I see the stuff people on here get excited about in these reviews though. "Can you see the BIOS through IPMI?". Thats the kind of thing Compaq offered back with the RILOE II and have been integrated into the motherboard since iLO 1 which is like 4 or 5 years old at least.
iLO4 on the Gen8 line have taken that a step further and we now hook the Display system BEFORE POST starts so instead of an invalid memory config getting you a series of beeps, you now get a full blown screen either on local VGA or on the Remote Console that straight up tells you you have a memory mismatch and why. i have seen his demo'd with NO DIMMs even installed in the server and you still get Video and obvious status messages.
Casper42 - Friday, August 10, 2012 - link
Also you are about $2000 high on the HP SL unless I am missing something.I found these prices with QuickSpecs part numbers and Google, nothing magical inside HP.
Half of one of these:
http://www.provantage.com/hewlett-packard-hp-62923...
Includes 8 fans and 3 PS
2 of these
http://www.provantage.com/hewlett-packard-hp-65904...
2x2665 with 8GB
Comes to about $11,600
JohanAnandtech - Tuesday, August 14, 2012 - link
Hey Casper, contact me on my mail... thx!ad99 - Monday, April 1, 2013 - link
You say：a quad rank DIMM with 4Gb chips is a 32GB DIMM (4 Gbit x 8 x 4 ranks)，but I think 4 Gbit x 8 x 4 ranks make only 16GB,is that right?ad99 - Monday, April 1, 2013 - link
No,4 Gbit x 8 x 4 ranks should be 128GB，not 32GB or 16GB,is that right?