AMD Radeon RX 6700 XT: Second choice for crypto mining

With the Radeon RX 6700 XT, AMD has presented the first graphics card to appear with the RDNA2 graphics chip Navi 22. While the Radeon RX 6700 XT is an attractive model for 1440p gaming, it is not the best choice for mining cryptocurrencies. Due to the generally poor availability of possible alternatives, however, they are also likely to be used in mining farms. Ethereum’s Ethash algorithm – currently the most lucrative cryptocurrency for mining with graphics cards – is always memory-limited. The constantly growing DAG (directed acyclic graph) now needs just over 4 GB and the faster the GPU can access the DAG in the graphics memory, the more hashes it can calculate per second. The shader processing power, on the other hand, is of secondary importance. AMD installs comparatively narrow memory interfaces in the RDNA2 graphics chips, supported by large, internal intermediate buffers – the Radeon RX 6700 XT, for example, uses 12 GB of GDDR6 on 192 data lines and 96 MB of last-level cache. This so-called infinity cache intercepts memory accesses in 3D games in order to increase the frame rate, which is less effective in Ethereum mining due to the random access to the huge DAG file. As a result, the hashrate decreases and with it the efficiency of the prospecting.
Even the Radeon graphics cards RX 6900 XT, RX 6800 XT and RX 6800 are quite slow compared to Nvidia’s RTX 3000 competition: AMD’s “Big Navi” manages around 63 megahashes per second (MH / s), Nvidia’s top model, when mining Ethereum GeForce RTX 3090, on the other hand, more than 120. A similar picture emerges with the Radeon RX 6700 XT: We measured a good 46 MH / s without much optimization effort. We increased the GDDR6 clock frequency by 100 MHz and underclocked the GPU to around 1100 MHz to reduce power consumption without the hashrate dropping. AMD’s driver limits the efficiency gain, since the GPU voltage of our sample can be manually adjusted to a minimum of 912 millivolts. With the automatic lowering due to the reduced GPU clock, you get at least 887 millivolts. The AMD graphics driver calculates a GPU power consumption of just under 120 watts – in addition, there are memory and converter losses of 20 to 30 watts, according to experience. According to the driver, the GDDR6 temperature climbs up to 103 degrees Celsius, i.e. just below the limit of 110 ° C, from which the SDRAM reduces its clock frequency.
The Radeon RX 6700 XT manages around 46 MH / s in Ethereum mining. However, the driver limits the undervolting.

(Image: Carsten Spille / c’t)
On the other hand, there is Nvidia’s GeForce RTX 3060, also with a 192-bit interface and 12 GB of GDDR6 memory, which manages around 45 MH / s with a real consumption of slightly more than 100 watts. The (hardly available) GeForce model costs 330 instead of 480 euros on paper.
As soon as the general availability of graphics cards improves, miners should prefer RTX-3000 models. Currently, however, the difference in efficiency hardly plays a role, as miners buy away pretty much anything they can get their hands on. Even expensive notebooks are used to mine cryptocurrencies. (mma)
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