Alex Turner wrote:
Spend a fortune on dual core CPUs and then buy crappy disks...  I bet
for most applications this system will be IO bound, and you will see a
nice lot of drive failures in the first year of operation with
consumer grade drives.

Spend your money on better Disks, and don't bother with Dual Core IMHO
unless you can prove the need for it.

I would say the opposite -- you always want Dual Core nowadays. DC Opterons simply give you better bang for the buck than single core Opterons. Price out a 1xDC system against a 2x1P system -- the 1xDC will be cheaper. Do the same for 2xDC versus 4x1P, 4xDC versus 8x1P, 8xDC versus 16x1P, etc. -- DC gets cheaper by wider and wider margins because those mega-CPU motherboards are astronomically expensive.

DC also gives you a better upgrade path. Let's say you do testing and figure 2x246 is the right setup to handle the load. Well instead of getting 2x1P, use the same 2P motherboard but only populate 1 CPU w/ a DC/270. Now you have a server that can be upgraded to +80% more CPU by popping in another DC/270 versus throwing out the entire thing to get a 4x1P setup.

The only questions would be:
(1) Do you need a SMP server at all? I'd claim yes -- you always need 2+ cores whether it's DC or 2P to avoid IO interrupts blocking other processes from running.

(2) Does a DC system perform better than it's Nx1P cousin? My experience is yes. Did some rough tests in a drop-in-replacement 1x265 versus 2x244 and saw about +10% for DC. All the official benchmarks (Spec, Java, SAP, etc) from AMD/Sun/HP/IBM show DCs outperforming the Nx1P setups.

(3) Do you need an insane amount of memory? Well here's the case where the more expensive motherboard will serve you better since each CPU slot has its own bank of memory. Spend more money on memory, get cheaper single-core CPUs.

Of course, this doesn't apply if you are an Intel/Dell-only shop. Xeon DCs, while cheaper than their corresponding single-core SMPs, don't have the same performance profile of Opteron DCs. Basically, you're paying a bit extra so your server can generate a ton more heat.

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