It's the Drive, Stupid! - more

For writing, there are many caches and buffers that hide the physical limitations of the drive(s). Figure 6 shows the write results of the same group of tests. I kept the vertical scale the same so that we can see the details of the non-cached performance. The relative results are remarkably similar to the read results, with the RAID 5 configuration losing the most steam as the effects of the cache in the iozone machine and 509 Pro run out.

Figure 6: Single drive write throughput comparison

Closing Thoughts

The exercise of proving out my new iozone test machine turned out to be more complicated than I expected because I was dealing with two unknowns: the test system and the target system that was being tested. This meant that I had to understand the results that I was seeing, especially when they were far from what I expected. (In the end, the drastically different results were a good thing, because they challenged my assumptions and made me do my homework!)

In the end, I probably had enough compute power in the old P4 based testbed. But the change to the PCIe gigabit NIC was definitely necessary to ensure that the network connection doesn't limit test results.

The other "lesson learned" through this exercise, that drive performance can affect NAS performance, actually was already learned through Bill Meade's investigation a little over a year ago. The main difference between then and now is the appearance of NASes with enough compute power, memory and networking performance to reveal the limits that drive performance can impose!

Next time, we'll see if Windows Home Server really deserves the reputation that it has garnered (from its fans, at least!) as a high performance NAS.

Tags: DIY, How To, NAS, RAID,

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