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I have Dell PowerEdge R210 II server with 4Gb of memory installed. And I also have 8Gb memory module. I replaced 4Gb with 8Gb – server is working ok. But mixing memory in different ways got error "Unsupported memory configuration. DIMM mismatch across slots detected".

How can I install them both to get 12Gb of memory?

P.S. From server documentation: "Memory modules of different sizes can be mixed in sockets 1 to 4 (for example, 2 GB and 4 GB), but all populated channels must have identical configurations."

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exactly what kind of memory modules do you have? two 2 gb modules, and one 8 gb module? –  longneck Oct 18 '12 at 15:00
    
one module of 4Gb and one module of 8Gb –  Dmitry Oct 18 '12 at 15:02
    
What are the specifications on the memory modules? Are both buffered or registered? –  Hennes Oct 18 '12 at 16:10
    
1) ECC, UNBUFFERED, 4 GB 2) ECC, UNBUFFERED, 8 GB –  Dmitry Oct 18 '12 at 16:12
    
According tp page 26 on <A href="google.co.uk/… Poweredge R210 II user manual</a> that is the right type of memory. The only point worth noting is that for dual rank memory modules with two modules per channel the max speed drop to 1066Mhz. I would expect the BIOS to fall back in speed though. –  Hennes Oct 18 '12 at 16:27
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2 Answers

you will notice that each of the slots is either white or black. the white slots are the first channel, and the black slots are the second channel. also, the manual implies that a channel can be unpopulated.

therefore, you should install your 2 ram modules in slots 1 and 3, i.e. the two white slots.

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The same error "Unsupported memory configuration. DIMM mismatch across slots detected" –  Dmitry Oct 18 '12 at 15:54
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I have a R210 II sitting here that's running fine using 24GB RAM (16GB + 8GB). No warnings or problems. Is your server running the latest firmware?

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