Testing the Gigabit LAN
So was this simple change enough to ensure that my iozone computer wouldn't limit my ability to fully test 100 MB/s NASes? I didn't have any of those around, but instead turned to the QNAP TS-509 Pro that I had recently reviewed. The 509 Pro has the most computing horsepower of any NASes tested to date combining a 1.6 GHz Intel Celeron M 420 Processor and 1 GB of DDR2 667 RAM.
A look at the comparative RAID 5 read performance NAS Chart plot (Figure 2) shows that the 509 Pro's performance is suspiciously flat while the next three top-performing products show typical variation. It didn't occur to me at the time, but the 509 Pro appears to be bumping up against some performance limit.
Figure 2: RAID 5 Read competitive performance - 1000 Mbps LAN
So I used the new iozone machine documented in Table 2 to run a few more tests. The TS 509 Pro was configured as it was in the review, in RAID 5 with five Hitachi Deskstar HDS721010KLA330 1 TB drives (7200RPM 3.0 Gb/s SATA 32 MB) that were provided by QNAP.
I connected up the new iozone machine and reran the tests, once with the onboard PCIe gigabit NIC and once with the same Intel PRO/1000 MT PCI-based gigabit NIC used in the old iozone machine. Figure 3 shows the results.
Figure 3: QNAP TS-509 Pro - Testbed iozone computer comparison
The plot also has lines for 100 and 1000 Mbps maximum theoretical throughput (12.5 MB/s and 125 MB/s) and actual results from the gigabit NIC testing shown in Figure 1 (marked 1000 Mbps LAN - PCI and PCIe). Note that jumbo frames were not used in any of the tests shown.
The two lower plot lines both use the Intel PCI-based NIC. I'm not exactly sure why the old iozone machine has lower throughput at the smaller filesizes, but remember we're talking two very different computers here. The old, a Pentium 4 with 512 MB of DDR 333 memory and the new, a Core 2 Duo E4400 with 1 GB of DDR 667 memory.
But the throughput lines converge from filesizes 2 MB on up, showing that the additional horsepower in the new iozone machine doesn't really affect the test outcome at larger filesizes. Note also that both lines are well below the tested 67 MB/s throughput of the PCI gigabit NIC.
The top trace is the new iozone machine with the PCIe onboard gigabit NIC. That result is closer to 70 MB/s; a gain of more than 10 MB/s over the other two runs. But it is still well-shy of the 113 MB/s of the PCIe gigabit Ethernet connection, which means that some other limiting factor is in play.