Workstation for number crunching: which RAM

[velvia]

Hi,

I am building a small workstation for number crunching. It is based upon:

- Xeon E5-1660v3

- ASRock X99 WS

- 4 sticks of Corsair Memory - 4GB (1x4GB) DDR4 2133MHz CL15 DIMM

It has been ordered but I still can cancel the memory. I am going to put 4 Memory stick on the main board, but what scares me is that I have realised that Corsair brands it as a Dual Channel memory ( http://www.corsair.com/en-us/corsair-memory-4gb-1x4gb-ddr4-2133mhz-cl15-dimm-cmv4gx4m1a2133c15 ). We have chosen this memory because the ASRock website says that is works as Quad Channel ( http://www.asrock.com/mb/Intel/X99%20WS/?cat=Memory ).

- Who should I believe ?

- Is it a good choice to put such memory for a number crunching workstation that needs high bandwidth? I have seen that there are faster memory (up to 3200 MHz), but the Xeon only support 2133 MHz memory which is why I have chosen this one. Any recommendation on RAM?

[McCalpinJohn]

You don't need to worry about whether the DIMMs are labeled "dual channel" or "quad channel" for the Xeon E6-1660v3 platform.   As long as they are the same size, speed, and organization the system should configure itself optimally at boot time (provided that you put them in the correct slots -- one per channel).

[velvia]

Hi John,

Thanks for your answer. Your nicknane seems to shiw that you are the right person to ask such questions.

If I may ask, on such a platform (X99), with a given processor:

- Does the main board affect the bandwidth? Is the ASRock X99 WS good enough?

- At a given frequency, is there a discrepency in bandwith between different RAM? Is mine good enough?

- Is there an advantage to use RAM that can be clocked above 2133 MHz with a Xeon E3-1660v3 ?

I do a lot of linear algebra, so bandwidth is important to me.

[McCalpinJohn]

The Xeon E5-1660 v3 does not allow the BIOS to program a DRAM frequency faster than 2133, so there is no point in paying for higher frequency DRAMs.

The DRAM CAS latency is a very small part of the total memory latency, so there is little benefit to paying for the lower latency memory at the same frequency.   The memory referenced above is CL15, which means that the CAS latency is 15 clocks.  For DDR4/2133 the clock is 1066 MHz, giving a clock period of 0.938 ns.  15 clocks is therefore 14.07 ns, and the more expensive CL13 memory is 12.2 ns -- about 1.9 ns faster.

I have not measured the total memory latency of the Xeon Haswells in the single-socket configuration, but it is probably in the range of 70 ns.  Not surprisingly, a difference of 1.9 ns in the DRAM CAS latency makes a very small fractional difference in the total latency.  (That is assuming that the BIOS actually programs the lower latency into the memory controller -- that is not guaranteed for server processors, which sometimes make more conservative timing assumptions than the data in the SPD on the DIMM.)

The motherboard will have minimal impact on performance for the Xeon E3-1660 v3.  Different BIOS's may provide slightly different "fine-tuning" capability, but this will almost always be a very small factor in overall performance for non-overclocked chips.

The only open issue is whether your codes will run better with dual-rank DIMMs than with single-rank DIMMs.   Given the price of the processor, the cost of going from 4x4GiB (single rank) to 4x8GiB (dual-rank) is a small increment -- about $30*4=$120 USD according to the Corsair web site.    More memory should help overall performance in almost all cases.

[Bernard]

>>> Is the ASRock X99 WS good enough?>>>

Do you mean a motherboard type or chipset?

I think that in your case motherboard from pure computational point of view is less important that CPU and/or memory.