Some thoughts about the SAP 8-socket benchmark at HP and Sun

I thought a while just write another comment about the HP785G6 benchmark in the comment section of the “Case Design” or the Do more with less” article. At the end i thought, this will be a fine article. At first: Yes, the benchmark of Sun used 256 GByte, whereas as the HP 128 GByte. At first this sounds like benchmark not comparable to each other. One of the basics in SoHo benchmarks is to compare benchmarks with the same memory size. The problem: You can’t use this knowledge here. But: The amount of memory just matters in SAP-SD when you don’t have enough. When you don’t believe me, ask your favorite vendor of IT equipment and ask for SAP-SD numbers with different memory sizes. The answer will be similar. To be more exact, the speed of the memory has a bigger impact than the size of the memory, given that you have enough memory. Another reader summarized it in a good manner: If HP could get a better result just by adding memory, they would have done it. It’s difficult to increase compute power when you are already using the fastest CPU. It’s difficult to increase the core count when you are already using the the CPU with the highest number of cores. But just plugging more memory into the system is easy. I haven’t heard any news about HP having a shortage of memory modules. But it think there is a different reason, why HP just used 128 GB. When you look at page 15 of the quick specs pdf of the HP DL785G6 speed you will find the following note:

When only PC2-6400 DIMMs modules are installed with a processor then memory bus speeds for 4 or fewer, 6 or 8 DIMMs per processor will operate at PC2-6400, PC2-5300 and PC2-4200 respectively. All other processor and memory configurations will operate at PC2-5300 with 4 or fewer DIMMs and PC2-4200 with

The largest memory flavor with PC2-6400 is “8 GB REG PC2-6400 2 x 4 GB”. The DL785 has 64 DIMM slots. To keep the memory bus at PC6400, you can just populate 32 of them. 32x4=128GB. They’ve ran the system at the top configuration that allowed them to use faster DIMMs. But you just to that, when you have enough memory in the smaller configuration, because the impact of having not enough memory is much larger than the impact of 133 MHz more memory speed. From this point it get’s even more strangely: The X4640 didn’s just had slower a slower CPU (200 MHz), it has also a tad slower memory (a X4640 use PC2-5300 for all memory configurations). This makes the difference between the systems even larger as suggested by the pure SAPS numbers. For the database something similar is valid. Roundabout 3-4% percent of an SAP-SD benchmark are database-bound and basic math suggests, that even a database 25% faster has a rather small impact on the database. Of course it would be nicer to have an exact proof by having benchmark results just differing by a single point but we have to live with it, that such results aren’t available. But Sun is in a nice situation here, when you look at the situation with some logic. The vast difference between the HP DL785 and the X4640 can be explained by three major points:

I think we can say that the third point can be erased from the list. I know HP as a competent company. As usual the an organisation of such a size is a victim of the bell curve, thus it has it share of dumb asses and outright geniuses. So your personal experience may differ, but let’s just assume that HP is competent enough to tune a SAP. So we are at:

Leaves us with “better OS” or “better HW”. Either way it’s nice for Sun and that’s exactly the reason why we won’t see an Solaris/DL785/Oracle result from HP. Such a benchmark could have two outcomes: The DL785 yields the same result than the X4640 or it delivers worse result. The first would show that Solaris is a better operating system than Linux, the second outcome would show that the X4640 is a better system. Both is positive for Sun, both outcomes are negative for HP. When the system is 25% slower, this would really kill the DL785. If Solaris is 25% better, then this would kill all the arguments that Linux is as scaleable as an enterprise Unix. If it’s a combination of both, well … then this just proofs that Sun has a more competitive package. I’m fine with all three outcomes. Of course you could ask “Why does Sun don’t deliver an Windows/Linux result?”. Well … honestly: Would you believe us? We have our own operating system and i’m sure the prefered excuse when the benchmarks with Linux or Windows are made by Sun would be “Sun didn’t tune Linux correctly, they just want to make Solaris looks good”. Of course Sun won’t make up the results, as this is too easy to detect and to confirm and would habe an horrible impact PR-wise. And at the end it’s HPs task to show that their system is comparable, not ours.