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Just wishing to confirm the old adage I'm holding to, is that for X memory on dual-cpu server, it better to have two X/2 sticks, as it enables each CPU to independently access said memory stick.

Was there any change with recent CPU's, or it still the same?

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It depends entirely on the server/motherboard and CPU type/numbers - there's not one-size-fits-all these days, let us know the details and we'll try to help. – Chopper3 Apr 4 '11 at 12:22
For example, Dell R410 standard configuration, with 2 6-core CPUs (E5646 and higher). – SyRenity Apr 4 '11 at 12:35
Consult with the server manufacturer or their agent. – John Gardeniers Apr 4 '11 at 12:52
As both Chopper and John say, no one-size-fits-all and also to check with your Dell rep. Our Dell rep mentioned that they have worked it out with these R*10s as to what your best performance can be with memory, and these change for each server. You may have 2 different size sticks, or you may not, in the server with them being in particular slots. – Chadddada Apr 4 '11 at 14:03
up vote 3 down vote accepted

For that particular model the best performance is reached by using identical DIMMs in EVERY slot - although this isn't necessarily the cheapest or most future-proof option.

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Dell R410 System Memory Configuration

Some recommendations:

  • Use registered DIMMS (RDIMM) - unregistered DIMMS are supported, but I wouldn't recommend them due to the small sizes
  • 8 slots are split in to 4 slots per processor with 3 channels per slot (2 DIMMS in channel 0, 1 DIMM for the other two)
  • In Advanced ECC mode, only 2 slots are available per processor (Channel 0), the other 2 are unused
  • Likewise, in Memory Mirroring mode, only 1 channel is used per process and 1/2 of the memory is not available due to mirroring
  • Optimizer Mode supports paired or odd numbers of DIMMS
  • Optimizer Mode also supports different sizes so long as the types match (RDIMM vs uDIMM)
  • The memory will run at the speed of the slowest DIMM installed
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This will vary on each situation depending on the motherboard. Generally, or more recently rather, the sticks will interleave to form a dual/triple channel. Meaning on the side for CPU1 you'll have memory slots 1,3,5,7 and on the side for CPU2 you'll have memory slots 2,4,6,8.

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This is clear of course, but in short you say that it still better to have 2 sticks instead of 1? :) – SyRenity Apr 4 '11 at 12:48
No this is not clear, the board you could be speaking of could be from when there was no dual channel. In short though, I'd suggest using 2 sticks for this purpose. – Split71 Apr 4 '11 at 12:55

As Chopper3 stated, every dimm slot sould be populated for optimal performance on that particular motherboard. Using 2 dimms will not be optimal but would be somewhat better than 1 dimm (if 1 dimm is even a valid config)

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