Do you remember how last year AMD Radeon R9 280X GPUs started dropping in terms of mining hashrate for Ethereum due to the growing DAG file size? Well, it seems that we are in for the same thing happening with the Radeon RX400/RX500 series of GPUs with 4/8GB VRAM in the next couple of months. We are currently at DAG epoch #129, but in the next 30-35 or so DAG epochs we are going to be seeing gradual drop in hashrate resulting in up to about 30% decrease from the current hashrate on the Radeon RX400/RX500 series of GPUs. It seems that other more powerful GPUs such as R9 290(x)/390(x) as well as Nvidia Pascal GPUs with more video memory (6GB/8GB+) will not be affected or the drop in performance will be much smaller to a level considered pretty much insignificant compared to what will happen with AMD’s Polaris GPUs.
You can easily check what will happen with your existing GPU mining hardware and if it will be affected in terms of performance and how much by adding the option
-benchmark 130 to the Claymore ETH miner. Change the number 130 (the next Ethereum DAG epoch) to the DAG epoch you want to test with such as 140, 150, 160 and see how your hashrate will change or if it will change. The Ethash DAG changes every 30000 blocks which is roughly every 4-5 days and with Ethereum this is called a DAG epoch, so every few days we move to the next DAG epoch. As DAG epochs move further on they also grow in size and put more stress to the video cards that are being used for mining and as a result there is also some performance drop observed over time. The more powerful the GPUs is and the more video memory it has, the more likely it is to be able to handle better long term mining Ethereum.