Comments (4)

By admin, April 12, 2012 10:13 pm

Say if I have ordered the latest Dell Powerdge R720xd with 2 sockets Xeon-E5 CPUs and fill it up with 768GB Ram (32GB x 24 Dimms). R720 supports 4 memory channels per processor, that’s 3 dimms per channel, so 12 dimms in total per processor, or 24 dimms per 2 sockets. In contrast, R710 supports 3 memory channels and 3 dimms per channel, a total of 18 dimms per 2 sockets.

Since vSphere 5.0 Enterprise Plus Licensing Model allows 96GB vRAM per socket, so that’s 192GB vRAM per the above configuration, this leaves the remaining 576GB vRAM in question. According to their licensing formula, I need to purchase 6 more EP licenses in order to fully use the 768GB Ram. Sounds strange that I need to have 8 CPUs license while the physical server only has 2 CPUs.

Let’s put the above extreme case aside, in reality not many is going to order that super expensive 32GB and no one is going to put that much ram in mid-range server like R720 as well anyway.

So let’s focus on the optimal memory configuration for R720, I would say it’s most likely to be 192GB (in fact 256GB).

Currently, mainstream is still 8GB ram, therefore for 192GB RAM, that’s 24 Dimms (8GB x 24), but with 3 Dimms Per Channel (DPC) configuration, it will decrease the RAM speed to 1066Mhz which I want to maintain RDIMM at 1333Mhz bandwidth and 1.35V, so in order to do that, I can only use 16GB ram and for 192GB, that’s 12 Dimms, an uneven number configuration, 3 channels per side, missing one channel, this sounds REALLY ODD?!!! Isn’t it a big drop in memory performance if we do not fill up all channels on each socket? (I might be wrong on this)

So if I insist to run at 1333Mhz, the only choice I have is to have 2DPC x 4 channels, that’s 16 Dimms x 16GB = 256GB, well, it’s over 192GB limit!

I really don’t know what else I can configure the memory in order to fully use 256GB ram with 2 VMware EP license. If you have any better suggestion, please let me know. Of course, if my assumption of fully using all 4  channels proved to be wrong later, then this won’t be a problem.

That’s why people are suggesting VMware to raise the bar to 128GB per socket, this would be perfect solution then, let’s see.

Oh…I just noticed NASDAQ:VMW had a free fall on Wed as their CFO jumped off the ship, is something going on under the table?

Comments (0)

By admin, April 12, 2012 2:21 pm

There is a very good article about DDR3-1600 Memory Configuration for Poweredge 12th Generation Servers, it’s good to see finally the 1U R620 having 24 Dimms as their big brother 2U R720. Also, I found a link regarding the latest LRDIMM, it’s very interesting as well.

On the eve of Intel’s release of Sandy Bridge-EP, the next generation of Xeon processors for servers, the memory industry has geared up for another uptick in memory speed.  Following Moore’s law– speed and performance are increasing while costs for memory are at historic lows.   Configuring servers for maximum power and performance has never been more affordable.

By selecting the latest DDR3-1600 (PC3-12800) speed DIMMs that deliver a data rate of 12.8 GB/s, you will realize about 20% more throughput than existing DDR3-1333 (PC3-10600) speed memory which delivers a data rate of 10.66 GB/s.   PC3-10600 RDIMMs, the most commonly used RDIMMs in today’s Xeon 5600 CPUs based servers, will give way to the faster PC3-12800 speed memory.

Just an FYI for the novice reader—the terms “DDR3-1333” and “DDR3-1600” are DRAM speeds, and “PC3-10600” and “PC3-12800” are MODULE (DIMM) speeds, as defined by JEDEC.  However many times, the DRAM speed nomenclature is used universally as both DRAM and DIMM speed indications.

AMD also has adopted the faster DDR3-1600 speed memory for servers with the introduction of Opteron 6200 “Interlagos” CPUs.   Servers and workstations will see significant performance improvements over prior generation Opteron 6100, which also featured DDR3-1333 as the top memory speed.

This discussion is all about speed and performance–since these DDR3-1600 applications will be offered at standard DDR3 1.5V power only.

Low voltage 1.35V (PC3L), and future 1.25V lower voltage dimms, will not be enabled at DDR3-1600 speed in this new generation of servers.

They will however continue to support DDR3L-1333 (PC3L-10600R) memory speeds at low voltage (1.35V), for those wishing to extract maximum power savings from their server infrastructure in lieu of the highest possible performance.   The trade-off decisions continue between maximum power savings vs. maximum compute performance.   The “tug-of-war” between “Going Green” vs. “My Servers are my Strategic Weapons” groups continues, with the power users configuring for maximum speed and competitive advantage by delivering the fastest response times.

Additionally, a new 32GB DDR3-1333 (PC3L-10600) LRDIMM (Load Reduced DIMM) is available now which is required for these servers to achieve a maximum memory capacity of 768GB.