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January 23rd, 2025 01:46
Dell t640 memory woes
System:
Dell t640 server
Dual 6240s
8x8GB sticks (model: HMA81GR7CJR8N-VK DDR4-2666 ECC RDIMM 1Rx8 PC4-21300V-R CL19)
Latest firmware
Having an issue with the memory, where all 8 sticks are populated and show up in iDRAC. But I only have a usable amount of 56GBs
I did switch the CPUs from the 5122 gold CPUs where all 64GB of ram worked.
Symptoms: Upon installing the new CPUs I kept getting a "Uncorrectable memory error" on slot A1, Once I reseated CPU1 it went away.
Attempted two memory populations. 1) A1,2,3,4/B1,2,3,4 and 2)A1,2,4,5/B1,2,4,5(Which it currently has now)
Yet has not resolved the issue. What would be my next troubleshooting steps? 
No Events found!
DELL-Young E
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January 23rd, 2025 02:18
Hello,thanks for choosing Dell and welcome to our community.
https://dell.to/42ropWg
dims should be populated 1/2/3/4
"Populate all the sockets with white release tabs first, followed by the black release tabs."
https://dell.to/3C8Yrw1
The issue occurred after you swapped old CPU with the new ones, most likely CPU 1 is faulty.
"Uncorrectable memory error" on slot A1 - could be issue with the memory or CPU
need to do isolation test
If the system is in warranty call support for assistance, otherwise use a common sense to rule our CPU or DIMM.
Hope this helps.
(edited)
Chino de Oro
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January 23rd, 2025 02:29
Whenever the issue happened after processors upgrade work was involved, I'd check for bent pins.
EddieSon
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January 23rd, 2025 11:14
@DELL-Young E thank you for your reply.
Few things, on the memory population, further down the page on the link you supplied, it states
Even when memory is installed in a1/2/3/4 and B1/2/3/4 the issue still occurs. So I'm confused on what Dells recommended memory population is supposed to be. I will note though, when bought, memeory was in it's current configuration of 1/2/4/5 before cpu swap.
I'll try the CPU/memory isolation testing
Thanks!
EddieSon
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January 23rd, 2025 11:15
@EddieSon correction to my comment above.
DIMM population update for Performance Optimized mode with quantity of 4 and 8 DIMMs per processor.
EddieSon
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January 23rd, 2025 11:16
@Chino de Oro both CPU sockets were checked, and no damage to be seen.
EddieSon
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January 23rd, 2025 23:58
I swapped the CPUs and re-seated RAM and was able to get all 64GB of ram working. This is solved. Thank you for your help @Chino de Oro @DELL-Young E.