All About BTC, LTC, ETH mining as well as other alternative crypto currencies
When we are talking about GPU-based mining rigs for crypto currencies it is common for PCI-E extenders (or risers) to be used in order to be able to put more video cards on a single motherboard and use not only the available PCI Express x16 slots, but the smaller x1, x4 and x8 as well that were originally not designed to be used by video cards. You would normally not want to use these smaller slots with less PCI-E lanes for video cards that will be used for gaming for example, but they are more than enough for mining. Up until recently you would use a x1 to x1 or x1 to x16 PCI-E raiser (Extended) with a short ribbon cable in order to utilize the smaller PCI Express slots for mining. But there is new and very interesting alternative available now – PCI Express x1-x16 USB 3.0 extenders.
We have picked up a few of these new extenders to try them out as they look better designed and built as compared to the ones using ribbon cables, no to mention that the newer USB-based ones also offer some good advantages. Now, before continuing with out experience and impressions we should make something clear – these extenders only use USB 3.0 cable for data transfer they still connect to PCI-Express slot on the motherboard one one end and have a PCI-E slot that you put the video card in on the other end. They use USB 3.0 cable for data transfer as it is a reliable solution for high-speed data transfer and with good quality cable that is shielded you can easily get 50, 60 or even 100 cm length of the cable without problems. We have picked up extenders that do come with a long 1 meter cable and they work problem free and allow you to place the video cards further away from the motherboard and other cards, so that you can get better airflow and cooling.
Aside from the additional length that can easily be up to 1 meter (up to 20-25 cm for ribbon cable extenders) these extenders are also powered, meaning that your motherboard will not need to provide any power over the PCI-E slot to the video card – all the power coming from the PCI-E slot of the extender is supplied by an external molex power connector, so you can safely use even video cards that do not have additional PCI-E power connector on their boards without worrying that you can overload your motherboard that is not designed to supply so much power over the PCI-E bus for multiple video cards. We have tested these extenders with cards with both no external PCI-E power as well as with models that do have additional power connector and they all worked just fine. Also tested with both Nvidia and AMD graphics processors and no issues with both types, though you should note that using Nvidia GPU such as the GeForce GTX 750 Ti with CUDAminer you will be getting a bit lower performance when using an extender (any kind of PCI-E extender). AMD graphics do not seem to have this problem, so the most likely reason is in the fact that you are using less PCI-E lanes for the video card and although AMD with OpenCL does not seem to have a problem, Nvidia with CUDA appears to provide a slightly lower performance.
So if you are using a GeForce GTX 750 Ti with stock frequencies and are getting 255 KHS for Scrypt mining with the card directly plugged in the motherboard, if you put it on an x1 PCI-E extender you might get slightly lower performance in the 240-245 KHS range. The same goes for results with the card overclocked, from about 300 KHS on motherboard you can expect 285-290 KHS when you are using a x1 PCI-E extender. Unfortunately to avoid that you need to use full x16 PCI-E slots and/or extenders and that could limit significantly the number of cards you can install on a single motherboard.
In short, we are really satisfied with the PCI Express x1-x16 USB 3.0 Extenders. They offer better build quality and reliability as compared to ribbon cable extenders. You also get more freedom for placement of the video cards thanks to the longer cables for better airflow and cooling performance. The slight drop in performance when using Nvidia-based graphics cards for mining with the extenders is to be expected, but might be resolved in future updates for CUDAminer for example.