A SQL Server Hardware Tidbit a Day – Day 24

For Day 24 of this series, I want to talk a little about some things to consider as you make the decision whether to purchase a two-socket database server or a four- socket database server. Traditionally, it was very common to use a four-socket machine for most database server scenarios, while two-socket servers were most often used for web servers or application servers. With the advances in in new processors and the improvements in memory density of the past four to five years, you may want to reconsider that conventional wisdom.

Historically, two-socket database servers simply did not have enough processor capacity, memory capacity, or I/O capacity to handle many more demanding database workloads. Back in 2007, a two-socket server would typically have been limited to about eight processor cores, 32GB of RAM, and two or three PCI-E 1.0 or 2.0 expansion slots, which made it much more challenging to run a large database workload on a two-socket server in the past.

Processors have gotten far more powerful in the last few years, and memory density has gone up dramatically. Modern two-socket servers have 24 memory slots, which means that you can have 384GB of RAM with affordable 16GB DDR3 DIMMs or 768GB of RAM with more expensive 32GB DDR3 DIMMs. The price/GB of 32GB memory modules is still about $39/GB compared to about $13/GB for 16GB memory modules, but the prices for the larger modules has fallen 25% in the last two months.

It is also possible to get much more I/O capacity connected to a two-socket server than it was a few years ago. The latest generation, two-socket servers that use the Intel Xeon E5-2600 series processor can have six or seven PCI-E 3.0 expansion slots, that each have twice the bandwidth of the older PCI-E 2.0 standard.

Because of how the way that the Intel Tick-Tock processor release strategy works, two-socket servers get the latest processor microarchitectures and manufacturing process technology releases significantly sooner than when these same advances show up in the four-socket space. Right now, two-socket servers have the 32nm Sandy Bridge-EP, while four-socket servers are still using the older 32nm Westmere-EX that has higher core counts but lower single-threaded processor performance.

This performance gap will be even wider in Q3 of 2013, when the upcoming 22nm 12-core Ivy Bridge-EP is released. Four-socket servers will finally get caught up somewhat in Q4 of 2013, when the 22nm 15-core Ivy Bridge-EX is released but Ivy Bridge-EX  will still have higher core counts and lower single-threaded processor performance than Ivy Bridge-EP. The gap will open up again, probably in early 2015, when Haswell-EP is released.

The final reason to think about this issue is the cost of SQL Server 2012 core licenses. If you can run your workload on a two-socket server instead of a four-socket server, you can save over 50% on your SQL Server core-based license costs, which can be a very substantial savings! Even with SQL Server 2012 Standard Edition licenses, the license cost savings would pay for a very capable two-socket database server (exclusive of the I/O subsystem).

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