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JD1410
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R720 - mixed memory configuration

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Hi,

I've R720 fully populated with 24x16 GB dual-rank RDIMMs = they have 384 GB total.

I'd like to upgrade them to 512 GB, but apparently if quad-rank DIMM is installed, the last bank in channel has to remain empty.

Is that correct?

If yes, is it possible to have one channel per CPU populated with 2x32 GB DIMMs and all remaining channels populated with 16 GB ones?

Or all 4 channel need to have exactly the same DIMM layout?

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RE: R720 - mixed memory configuration

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One more question - it seems that following the rules, the only way to increase total memory for host fully populated 24x16 GB is to remove ALL 16 GB DIMMs and replace with 16x32 GB ones?

Yes, that sounds correct. You would need to swap out all memory with 32GB modules to increase the total memory since you are losing access to 4 slots due to quad rank memory.

Thanks

Daniel Mysinger
Dell EMC, Enterprise Engineer

Get support on Twitter @DellCaresPRO

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RE: R720 - mixed memory configuration

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Hello

Is that correct?

If quad rank memory modules are installed then the last channel(green) should not be used. So, if you use quad rank memory only slots 1-8 should be used.

Or all 4 channel need to have exactly the same DIMM layout?

All 4 channels are not required to have identical configurations, but in order to populate a module in a channel the previous channel cannot be empty. For instance, if you populate memory in slots 1,2 and leave 3,4 empty then you can populate memory in slots 5,6. You cannot put memory in slots 7,8. Also, quad rank and large memory modules are supposed to be populated before lower rank and smaller modules.

The R720 supports flexible memory, so many of the memory population rules can be broken. There is no supported configuration to populate the memory how you are wanting. You can review the population rules in the manual.

www.dell.com/support/home/product-support/product/poweredge-r720/

Thanks

Daniel Mysinger
Dell EMC, Enterprise Engineer

Get support on Twitter @DellCaresPRO

JD1410
1 Copper

RE: R720 - mixed memory configuration

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Thank you Daniel!

I'm planning following setup:

channel 0 (32, 32, 0)

channel 1 (32, 32, 0)

channel 2 (16, 16, 16)

channel 3 (16, 16, 16)

with the same for another CPU.

Can you please confirm that this is valid configuration? In order to further expand memory, I will have to replace 16 GB DIMMs, because it is not possible to use last banks in channel 0 & 1, correct?

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RE: R720 - mixed memory configuration

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I'm planning following setup:

channel 0 (32, 32, 0)

channel 1 (32, 32, 0)

channel 2 (16, 16, 16)

channel 3 (16, 16, 16)

with the same for another CPU.

Can you please confirm that this is valid configuration? In order to further expand memory, I will have to replace 16 GB DIMMs, because it is not possible to use last banks in channel 0 & 1, correct?

No, that is not a valid setup. I explained in my previous post that is not a valid setup. If you only have 2 modules populated in channel 0 then the rest of the channels can only have 2 modules as well. The memory may function in the configuration you are proposing, but it would not be a supported configuration. You would likely receive a warning message about the configuration if it does work.

Thanks

Daniel Mysinger
Dell EMC, Enterprise Engineer

Get support on Twitter @DellCaresPRO

JD1410
1 Copper

RE: R720 - mixed memory configuration

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Thanks for clarification - I thought that I only can't populate last slot within given channel, not that any green slot can't be populated.

So it seems only supported way to increase memory in the host is to replace all 16 GB DIMMs with 32 GB quad-rank ones (because if I have to remove 16 GB DIMMs from green slots, then I am not getting any increase from current setup).

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RE: R720 - mixed memory configuration

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It is much easier to work with memory by slot number and groupings or banks than by channel. The groupings by slot are:

1,2,3,4
5,6,7,8
9,10,11,12

Your proposed configuration is populating slots:

1,2,3,4
5,6,7,8
11,12

There are three reasons your proposed configuration would not be supported. Reason #1 is because slots 11,12 should not be populated unless slots 9,10 are populated. If you were using only your 16GB 2R modules then moving the modules from 11,12 to 9,10 and leaving 11,12 empty would be a valid configuration.

Reason #2 that the configuration is not supported is because you are mixing memory within a memory grouping. All memory within slots 1-4 should be identical. The same goes for the other two groups of memory. Putting 32GB modules in 1,2 and 16GB modules in 3,4 would not be a supported configuration.

Reason #3 is because when you use quad rank modules only the first two slots within a channel can be used. That means if you use quad rank modules you can't use the green slots(9,10,11,12).

Flexible memory allows many population rules to be broken. Not all population rules can be broken.

Thanks

Daniel Mysinger
Dell EMC, Enterprise Engineer

Get support on Twitter @DellCaresPRO

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JD1410
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RE: R720 - mixed memory configuration

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Thank you for the detailed explanation!

One more question - it seems that following the rules, the only way to increase total memory for host fully populated 24x16 GB is to remove ALL 16 GB DIMMs and replace with 16x32 GB ones?

Because it seems mixed supported configuration is only possible as:

32 GB 1,2,3,4

16 GB 5,6,7,8

But this only gives us the same total amount as we have right now (384 GB).

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RE: R720 - mixed memory configuration

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One more question - it seems that following the rules, the only way to increase total memory for host fully populated 24x16 GB is to remove ALL 16 GB DIMMs and replace with 16x32 GB ones?

Yes, that sounds correct. You would need to swap out all memory with 32GB modules to increase the total memory since you are losing access to 4 slots due to quad rank memory.

Thanks

Daniel Mysinger
Dell EMC, Enterprise Engineer

Get support on Twitter @DellCaresPRO