R820 w/4CPUs ... How many 8GB modules can be installed?

Hello

Yes, you should be able to use all 48 slots. If you are using unregistered/unbuffered modules or quad rank modules then you can't use slots 9-12 on any of the memory risers. You appear to be using single rank registered/buffered memory, so you can use all slots.

The optimal configuration would be to use the same modules and populate all of the remaining 16 slots. You should be able to add less than 16 modules as well, as long as the amount is divisible by four. All of the memory risers should have identical memory configurations, so adding 10 modules would not be supported. There is no way to populate all four risers the same with 10 modules. 4, 8, 12, or 16 modules should be possible. I would not populate a single module in each riser, but it will probably work.

Populating slots 9-12 will reduce the maximum memory transfer rate from 1600 to 1333. Also, if you populate different size modules or do not fully populate all channels it may further reduce performance. All of this should be documented in the R820 manual. You can find documentation on the system support page.

http://www.dell.com/support/

Thanks

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@DELL-Daniel My wrote:

Hello

Yes, you should be able to use all 48 slots. If you are using unregistered/unbuffered modules or quad rank modules then you can't use slots 9-12 on any of the memory risers. You appear to be using single rank registered/buffered memory, so you can use all slots.

The optimal configuration would be to use the same modules and populate all of the remaining 16 slots. You should be able to add less than 16 modules as well, as long as the amount is divisible by four. All of the memory risers should have identical memory configurations, so adding 10 modules would not be supported. There is no way to populate all four risers the same with 10 modules. 4, 8, 12, or 16 modules should be possible. I would not populate a single module in each riser, but it will probably work.

Populating slots 9-12 will reduce the maximum memory transfer rate from 1600 to 1333. Also, if you populate different size modules or do not fully populate all channels it may further reduce performance. All of this should be documented in the R820 manual. You can find documentation on the system support page.

http://www.dell.com/support/

Thanks

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Thanks for the prompt reply!

Yes, we have already tried to install 48*8GB modules (it was an upgrade from the initial 16*8GB modules configuration), however. after two days after the installation we have encountered a fatal ECC problem with 3 modules in the same memory channel (B3/7/11). Simply removed  (not changed or reallocated) 16 modules out of 48 - and it now works. The slots in use are A/B/C/D 1...8.

So if you do not see an issue with using 40 (10 per CPU) or 44 (11 per CPU) modules, then we will try again. Thanks for noting that using 10 more modules is a bad idea.

What is documented: the best I can find is R820 Owner's Manual with some samples. What is not clear is what to do if you want to use more >32 modules (of the same size, for simplicity), but < 48 modules. Do you know a better / more detailed source?

No, I'm not aware of anything that has more information. There are memory articles about 12th generation servers that may explain how the memory works in more detail, but those documents will not be specific to the R820.

The manual should have all of the population guidelines listed. All possible memory populations are not listed in the manual or any document I'm aware.

Thanks again!

If we will be adding 8 modules: what are the better slots to use - 9/10 or 11/12?

You should populate lower slots first, I'm not sure if it would allow 11,12 if 9,10 are not populated. Put them in 9,10.