The R9 295X2 from AMD is a very interesting proposition for a miner. A few months ago, I’d have told you it was the single best card you could buy. Today I’m not so sure.
A few months ago, I set about buying up as many R9 295X2 cards as I could get my hands on. At the time I was mining ZEC, and the 295X2 promised a fairly major 660H/s. More importantly it offered that in a single motherboard slot, and with a respectable 400w of power use. The cards were really past the point of being the “best graphics card ever”, and the wealthy individuals who had bought them up at their original price point of £1500 were now selling them off in favour of Nvidia Titans and GTX1080 cards. Interest in them was low and ebay auctions were ending around the £230-£250 mark. I was able to get my hands on 3 at that price.
At the time they were spitting out around £10 per day of reward, so they were paying for themselves within a month. All in a single slot? Amazing.
A little down the line, the rest of the community has figured out that these cards are amazing for mining, and prices have shot up to around £650-£700 on ebay. The rewards have also thinned out, to around £7/day. So the payback period is now up to 100 days, plus electric cost. In addition the cards will probably depreciate back down to the £250 mark as difficulty on the current altcoins increases faster than the coin values. That being said, while mining Eth, as the DAG file size increases mining speed will drop off on cards lacking in memory, such as the R9 280X which is already no good for ETH at 2GB. The 295X2 card is an duel 4GB card, so should stay viable as a miner far longer than almost any other card you can buy, which is a major plus and probably the main thing pushing these high ebay prices.
But lets look at more reasons why maybe these cards are not the diamond they look like.
You need a 1050w+ quality power supply to get a pair of these to hold stable. Even on a brand new Corsair 1000w, I had stability problems and had to move to something beefier. Those power supplies are expensive, normally in excess of £150. Meanwhile I can power 3 RX480 cards from a Cooler Master 700.B power supply which I was picking up at £45 each before the mining boom. So the “PSU/Card” cost is around £75, rather than £15. Not a huge deal as PSUs hold a lot of their value and are easy to resell, but still a point worth noting.
Then there are driver issues. If you’re mining on Linux, good for you. If you’re on Windows 10, good luck. Windows 10 has a bad habit of pushing driver updates down on you, even after you’ve disabled the hardware update option. The latest ATI drivers (17.1+) with the R9 295X2 cause a bug where the card throttles down to 300MHz and stays there. Driver clean ups and reinstalls don’t fix it. Clockblocker might fix it for you if you’re lucky- but it didn’t work for me. The only solution I’ve found is a complete OS reinstall. Interestingly this bug does only seem to have happened on rigs where I’ve installed MSI Afterburner. Maybe that’s just a coincidence, but it’s worth being aware of.
Then lets talk about heat. A pair of these will push out 800w worth of heat. That’s about the equivalent to 5 RX480 cards. Make sure you’ve thought about how you’re going to keep the room cool. The addition of offboard 80mm cooling fans also makes them awkward to fit into most cases- a standard ATX case will have provisions for only one or two of these fans. So you’re going to need a totally custom mounting solution.
So is the R9 295X2 a bad card for mining? Well, no it’s a great card for mining in many ways. You’re looking at 660H/S ZEC, or around 55-60MHs in Eth. Great! The huge 2x4GB of memory should help keep it relevant for a long time. But before you go out and drop £700 on one on ebay, make sure you’ve done the maths, a pair of R9 290X cards maybe a good alternative. Oh and Windows 10 is bad, but you probably already knew that.