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is there a rule of thumb about this? should I get an older 4 chip server with dual-cores or a newer dual chip server with quad-cores?

I'm leaning towards the latter but thought I'd ask anyway.

Thanks.

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3 Answers 3

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All other things being equal I'd go for the 2x quad core option, as they will share L2 and L3 more effectively, but there are other things to consider that might not be equal such as:

  • How much L1/L2/L3 cache is available in to each core, each chip, and in total? You might find there is more cache in total in the multi chip arrangement and depending on the servers workload this may be significant.
  • What is the memory sub-system in general? (the newer system may have a better memory controller and faster RAM to go with it)
  • What speed do the chips run at? Depending on your exact workload pattern a difference in the performance of each individual core may be as (or more) significant as a difference in core arrangement. Remember to try get a measure of the speed in a true-ish benchmark (don't just go on clock speed as two core designs may perform differently clock-for-clock)
  • Do the two options have the same IO subsystem, or are there differences? For a large database server IO performance is often a far more important consideration than CPU+RAM performance.
  • What are the licensing terms you operate under for MSSQL? (if you have some sort of site/corporate/other bulk license this may not be an issue but if you are paying per CPU, which is often the case, the 4x dual core option will be significantly more expensive)
  • What edition of SLQ Server do you intend to run? I'm guessing Enterprise or Standard in which case it is not an issue (standard will use up to 4 CPUs and enterprise is not limited in that respect), but some editions will ignore all but the first CPU or two (see this and this - though those two pages are not clear on the fact I believe the limits are counting whole CPUs not individual processing cores)
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The MS SQL Server licensing model is based on CPU. You're going to be much better off with a Quad core setup. The new quads also have a better and more efficient architecture so you'll see more performance out of each core. You'll also be saving on power costs as 2 quad cores use less wattage than 4 dual cores.

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You should also consider that modern CPUs can do more work per clock cycle than older ones. So configuration and clock speed should not be the only considerations when choosing CPU for a database server. –  Mark Allison Jan 6 '10 at 14:39

If you're going for CPU-licencing for MS SQL server then you HAVE to go with the latter, dual-CPU quad-core setup purely from a licensing cost perspective, it may well be quicker but forget that for now - just go that way :)

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