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I am upgrading my HP ProLiant ML330 G6 (Single Processor) server to 48GB registered RAM.

Basically, I have done a bit of research and had come to a conclusion that 6 x Single Rank 8GB ECC RDIMMs were ideal for my upgrade.

However, after using the ProLiant Memory Configuration tool from HP, I am now a bit confused. The tool recommends using 3 x 16GB Quad ranks for performance as the first option, followed by 6 x 8GB Dual ranks as a second option.

From what I understand (please correct me if I'm wrong) that higher ranks pack denser memory per DIMM and from what I have read this is to enable the user to upgrade further in future without spending too much but at the cost of some bandwidth, which is why I decided to go the single rank. So using 6 x 8GB Single Rank DIMMs is meant to be faster than using 3 x 16GB Dual Rank DIMMs..

So my question to anyone with experience, should I go with the 6 x Single Rank 8GB or 3 x Dual Rank 16GB RDIMMs for best performance/bandwidth (without the need to upgrade anymore in RAM in future)?

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  • Supported Memory Speed in this model Server also depends on which CPU is installed. How many years are you planning on using this server? FYI The newer servers are notably more power efficient.
    – StackAbstraction
    Commented Sep 10, 2015 at 5:57
  • @StackAbstraction the server has an Intel® Xeon® E5500 series Quad Core single CPU, 9 DIMM slots total. I had purchased it from a third party source who initially had 16GB UDIMM (unbufferred) RAM, which IMO wasn't equally distributed along all channels and it felt very slow. And I am not planning on running the server for too many more years, I just need the best performance possible, without the need to increase more RAM in future.
    – Magic Mick
    Commented Sep 10, 2015 at 23:14
  • Which particular model E5500 series CPU and what speed ram are you aiming to use?
    – StackAbstraction
    Commented Sep 10, 2015 at 23:41
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    CPU is Intel® Xeon® Processor E5506 2.13 GHz, 4MB L3 Cache, 80W, DDR3-800. The RDIMMs I am looking to get are rated at 1600Mhz 1.5v (Kingston model. KTH-PL316S/8G), but obviously they wont be running at that speed @ 2 per channel.
    – Magic Mick
    Commented Sep 11, 2015 at 0:06
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    Ouch that CPU is stuck at 800 Mhz not the 1066/1333 MHz the system supports. Depending on your workload a CPU upgrade may be a nice boost as well.
    – StackAbstraction
    Commented Sep 11, 2015 at 0:12

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Either way you really can't go wrong unless you are expecting to upgrade again in the future (then go for higher density). No I don't expect you will see any real performance difference. EDIT Updated Dec 2012 HP GL330 G6 QuickSpec

So to sum up everything, it appears that ranks have more to do with density and pricing than actual performance. ... Keep in mind that most servers are upgradeable and RAM density [is a big] factor. It's best (albeit more expensive) to get the more dense RAM for servers to make room for future upgrades. dimms-single-vs-double-vs-quad-rank

Edit: Here is a deep dive into Memory Ranks and performance

He reports dual rank as long as you don't need to drop the Speed Rating of the RAM (from 1333 to 1066) would give you a small edge in performance. 1 DIMM per channel is ideal. Dual Rank allows more interleaving across DIMM modules and across ranks. i.e. 3 x 8GB Dual Rank RDIMM.

You could even use the Intel VTune Performance Analyzer to do memory bandwidth testing if desired.

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  • Thanks for that. This guy says differently when it comes to ranks, the lower the ranks, the better the performance? youtube.com/watch?v=ZBacS4x-Wjo
    – Magic Mick
    Commented Sep 10, 2015 at 23:25
  • Wow that video is a laugh and he contradicts himself in his own comments, toy cars on a race track, wow.
    – StackAbstraction
    Commented Sep 10, 2015 at 23:47
  • I think we are talking about maybe 10% memory performance at most => (less than) 3% typical real world application performance.
    – StackAbstraction
    Commented Sep 11, 2015 at 0:15
  • Judging by page 31 of that manual, I'd probably get them running at 1066Mhz. Also, looks like the higher the rank the lower the speed (Mhz) ? A quad rank 4GB chip would run at 1066Mhz whereas a Dual rank 4GB would run at 1333Mhz (single DIMM per channel). So Maybe I should just stick with my single rank purchase for better performance.
    – Magic Mick
    Commented Sep 11, 2015 at 0:19
  • You are stuck at 800 mhz with that E5506, if you have the budget an ebay E5540 Xeon 2.5Ghz support 1066 ram is $10 shipped. Check into upgrade to dual CPU (need to get fans/heatsinks) cheap.
    – StackAbstraction
    Commented Sep 11, 2015 at 0:25

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