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I have a Dell Poweredge R710. Right now it has 12 2GB, Cl=6 (per SIW), dual ranked, PC3-8500 RDIMMs running in Advanced ECC mode. I'd like to add 24 additional GBs.

I found this:

http://www.crucial.com/store/mpartspecs.aspx?mtbpoid=554271D7A5CA7304

(Dual Ranked, 4GB, RDIMM, PC3-10600, CL=9). I was thinking about getting 6 of these 4GB RDIMMS. My question:

Will adding the CL=9 RDIMMs cause a significant performance hit?

The server is running Server 2008 R2. It's primary purpose is to host a bunch (~5) of Hyper-V VMs.

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When you mix RAM your system will operate at the slowest speed of the RAM you have installed.

This link should be useful to you: http://www.dell.com/downloads/global/products/pedge/en/server-pedge-installing-upgrading-memory-11g.pdf

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I'm talking about timings not speed. I've ready the manual, but my question isn't answered. What I want to know is if a difference in timings like that one described is enough to cause a real world noticeable difference? –  user426724 Sep 26 '11 at 20:50
    
After reading into this a bit more I found that you are going to have to switch your type from "Advanced ECC mode" to "otpimized" mode in order to use the third memory channel properly. See this document: dell.com/downloads/global/products/pedge/en/… –  Dave Sep 27 '11 at 0:09
    
As for timing you likely will not feel the difference. The size increase will be the big win in this case if you are good with the change described above. –  Dave Sep 27 '11 at 0:23
    
Thanks! With memory I'm never sure what the relative importance of the factors is (i.e i can can compare specs and say "hm 6 is lower than 9, I guess that's better" but I don't have a real sense of how significant that better was is. In this case it sounds like more memory far outweighs performance hit from higher latency. Thanks again! –  user426724 Sep 28 '11 at 3:17

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