Dell T610 Memory configuration

Hey guys

It gets a bit frustrating trying to figure out the memory configurations that are possible on a server so I would really appreciate some input here.  Please do not send me a link.  I have looked at all of them and it just drives me nuts :-)

Here is what I have.  Dell T610 with dual CPU's.  all 12 slots of memory are filled with 4 gigs in each one.  I would like to replace them with 8 gig chips but the upfront cost of replacing all 12 is out of my personal budget right now.  I am using the memory configuration that allows me to access all 12 of the chips (the others are memory mirroring and something else that only looks at a few of them and I guess parity's the rest).

So, is it possible with the configuration I have to replace 1/2 of the chips or some other combination that will allow me to have more memory but not cost me an arm and a leg?
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You must have 2 CPUs if all 12 slots filled, you can replace any of the 4GB DIMMs with 8GB DIMMs assuming they are RDIMM but replacing a single one would be be very unbalanced and give NUMA nodes don't match type errors. Replace one from each CPU with an 8GB stick though and that'll work whichever slot you use, mixed memory configurations work fine.

Why 8GB sticks though? You gain 4GB by buying an 8GB stick for £64. Go for 16GB stick you gain 12GB for £135. 16GB sticks almost exactly* same price per GB as 8GB sticks but you throw less of those old 4GB sticks out if you use 16GB ones.

Recommended to buy any even number of 16GB sticks (24GB gained per pair of sticks).

* Oxymoron alert ;)
jonmenefeeAuthor Commented:
That is great news. So. I can replace one from each cpu and it will be cool. Best news I have heard all day. So I will buy 2 16 gig sticks and as long as they are the same speed as the others I can put one on cpu1 and the second on cpu 2. :-)   THANKS!!
jonmenefeeAuthor Commented:
Oh. And of course leaving the other 10 4 gig chips in place. :-)
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Yup, speed doesn't matter either as it will clock down to lowest common denominator.

RAM speed doesn't make much performance difference except for gaming PCs and HPC weather forecasting. For commercial apps such as those run under VMware or SQL databases quantity of RAM matters, speed doesn't.

Only real rule is you cannot mix UDIMMs with RDIMMS. If your current RAM is UDIMM you're really stuck but probably it is RDIMM. You may have to upgrade to latest firmware first as someone from Dell misunderstood the Intel manual and imposed unnecessary rules at one time.
jonmenefeeAuthor Commented:
Thank you for clarifying the UDimm vs RDimm.   I hope I have RDimm :-)
Late to the party, but this one has been on my radar.

I agree that reading the memory configuration chapter in the manuals is pretty daunting.

(Your 4GB modules are RDIMMs if they came from Dell with the server.)

As I read it, the Dell manual recommends you replace 6 DIMMs, either 16GB or 8GB should work. The larger-capacity DIMMs should go in the lower-numbered slots, i.e. A1 A2 A3 and B1 B2 B3. Note the DIMM sockets are not sequentially numbered on the motherboard.


Andy Alder may have it right, that evenly populating the slots doesn't matter, but I'd seek additional confirmation before purchasing just 2 DIMMs.
jonmenefeeAuthor Commented:
Thanks. :-)
Dell recommend evenly population but that's because of the results Intel generate using the STREAM memory benchmark test. Fujitsu deliberately mis-balanced one of their machines and did the STREAM benchmark along with the SPECint benchmark. Result - STREAM performs badly if unbalanced but SPECint hardly shows any performance degradation. (sorry about the link).

Table from that test page Page 14 (19)

Advanced 1.00 0.81 0.57 0.29
Standard 1.00 0.80 0.55 0.28
Basic 1.00 0.87 0.64 0.33

Advanced 1.00 0.97 0.91 0.74
Standard 1.00 0.98 0.93 0.79
Basic 1.00 0.99 0.98 0.89

The STREAM result shows a single DIMM to be one third of the speed of three DIMMS,
The SPECint result shows a single DIMM to be 0.89 of the speed of three DIMMs.

Commercial apps are like SPECint, not like STREAM so that's why unbalanced configurations are fine even though the vendors don't recommend it.
jonmenefeeAuthor Commented:
That is very cool information.  Thanks Andy.  :-)
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