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External Graphics Over PCIe 3.0? Netstor's NA255A, Reviewed

Setup And Overcoming Issues

In theory, populating the NA255A should be as easy as dropping in graphics cards, connecting their power leads, and hooking the external enclosure up to the host PC's PCI Express card. The TurboBox is designed to extend standardized interfaces, so no software driver should be necessary. In the real world, though, setup isn't quite that easy.

We encountered a couple of snags along the way. First, I initially didn't realize that the PCIe-based interface cards have specific I/Os. If you look closely, one port on each card is etched with a x16 and the other is etched with a x8. I accidentally hooked the x16 up to the x8 and vice versa. The mistake was easy to reverse, but it doesn't appear to be mentioned anywhere in Netstor's documentation.

The second hang-up was a little more worrisome. Mainly, I couldn't get the TurboBox working at PCI Express 3.0 signaling rates. First- and second-gen PCI Express worked fine. But when the jumped was set to PCIe 3.0, the enclosure stopped recognizing the graphics cards I was plugging in. Netstor helped us work through the issue, which involved reconfiguring switches on the interface cards. This solved our issue.

Our third issue wasn't the TurboBox's fault at all. During our first round of benchmarks, we saw odd performance drops with three Radeon HD 7970s installed. Much troubleshooting revealed that some of our Tahiti-based boards weren't working together the way they should have. It turned out that boards from different vendors shipped with incompatible firmware, which hampered multi-card configurations (even though this should have been fine). Mixing and matching products, even those from the same family, is asking for trouble. Fortunately, we worked around the problem with a different card combo.

Finally, we weren't able to test four Radeon HD 7970s at the same time. Again, this wasn't Netstor's fault, however. The TurboBox is absolutely able to accommodate a quartet of dual-slot boards. But because some of the 7970s in our lab are a little larger, they don't fit into the strict space limitations of two expansion slots. As a result, we're testing with three Radeon HD 7970s. It all works out, though: the ASRock X79 Extreme9 motherboard I'm using only has room for three 7970s anyway, so that's our hard limit for comparing native on-board connectivity to the performance of Netstor's device.