Archive for the ‘Mining Hardware’ Category

pci-express-x1-x16-usb-30-extender

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.

geforce-gtx-750-ti-power-usage-test-setup

The GeForce GTX 750 Ti series of graphics cards based no the new Nvidia Maxwell architecture have really captured the attention of crypto currency miners due to their good performance (hashrate) per watt. Nvidia is advertising these cards to have 60W TDP, however we have discovered that the actual TDP limit for the power target set in the video BIOS of these cards is 38.5W…

geforce-gtx-750-ti-power-usage-results

This made us dig into the matter a bit more in order to see how much power actually does a GeForce GTX 750 Ti draw from the motherboard (a reference GT 750 with no external PCI-E power connector). So we’ve attached a watt meter to the power line of an external PCI-E extender to see how much power is drawn by the GT 750 Ti card. The results we got were quite surprising, even though we knew that the default power consumption should fit in the 38.5W limit for the power target set in the BIOS. With the stock frequencies for the GPU and the video memory the GeForce GTX 750 Ti has shown to draw just about 28W ot power producing about 250 KHS hashrate for Scrypt mining. After getting the card overclocked to +135 MHz for the GPU and +650 MHz for the video memory the power consumption has risen a bit to about 34W average with a hashrate of about 300 KHS for Scrypt crypto mining.

So if you were calculating the power usage of GTX 750 Ti as 60W in order to see the ratio of hashrate per Watt of power, then you should rethink how you calculate it now. Note that this is the actual power that goes from the PSU to the video card, the real power consumption with a 80 Plus certified power supply that provides 90% efficiency for example would rise with 10% to about 30W (stock) and 37W (overclocked) respectively as the actual power drawn by the card from the wall socket.

dualminer-usb-scrypt-asic

This week we have finally received a DualMiner USB Scrypt ASIC based on a single Gridchip GC3355 processor that is capable of mining both BTC and LTC or only LTC (SHA-256 and Scrypt), so we can share some of our first impressions already using the device for a day. The device uses a dip switch to switch between the mode active at the moment (LTC and BTC and LTC Only) and there are two virtual COM ports available – one for BTC or other SHA-256 and one for LTC or other Scrypt crypto mining (you need to install a virtual USB to COM driver from here). When you are in BTC and LTC mining mode you are supposed to get about 500 MH/s for SHA-256 (BTC) along with about 40 KH/s for Scrypt (LTC), however we are and you are also probably going to be more interested in the performance of the LTC (Scrypt) mining mode only as this way the ASIC uses less power and provides more performance and you better go with 70 KH/s LTC instead of 40 KH/s LTC and 500 MH/s BTC nowadays. One important thing is that when the device is in LTC mode only you need to use the BTC COM port (the first one) and when operating in Dual mode the first COM is for BTC and the second for LTC.

cgminer-dualminer

DualMiner USB Scrypt ASIC uses a modified version of cgminer that comes along with an extra GUI that might be more appearing to the new to mining users, however we prefer to use directly the cgminer from the console (version 3.1.1). The extra parameters you are passing to the cgminer include “–lo” for the LTC only mode (Scrypt only), “-S //./COM12” to set the COM port used by the device and “–dualminer-pll 850” to set the operating frequency of the chip. When you switch to LTC mode only the ASIC increases the voltage to 1.2V and uses 850 MHz to achieve 70 KH/s, in BTC & LTC mode apparently the voltage is 0.9V and the clock frequency is 550 MHz for 500 MH/s and 40 KH/s respectively. You can try increasing the MHz value a bit to about 900 to squeeze a bit more performance, though you should be careful as not all devices apparently can work at that frequency and you better have some sort of extra cooling.

dualminer-scryptguid-hashrate

Our tests show that when the device is used in a pool, the reported hashrate is a bit above 70 KH/s, the screenshot is from ScryptGuild with difficulty set to 16. You need to set the difficulty for the worker lower in order to get good actual performance due to the not so high hashrate of these miners. For the first 24 hours our DualMiner USB Scrypt ASIC has managed to get away with just about 0.15% HW errors running at 850 MHz with an extra fan for better cooling, s things are looking pretty good. We are going to perform some more tests and publish them here in the next few days, so stay tuned for more information abut these USB ASICs based on Gridseed’s GC3355 chips. And while we like how things are working with this low power Scrypt ASIC, we are not going to recommend the purchase of single units due to the low hashrate that each device provides and if you are going to invest in more of these USB ASICs, then you might want to check out the 5-chip Gridseed miners supposed to offer 300 MH/s per devices – these will cost you less for the same total performance. For the moment the price at which the DualMiner USB ASICs are being sold they are not that attractive choice, and we have ordered one just to play around with it. We are waiting for one of the larger 5-chip units to arrive in the next few days, so we are going to be reviewing it as well soon.


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