Now that the excellent Radeon 7950 video cards have essentially become unobtainable, I’m getting a lot of questions from people about how to get the most out of the new Radeon R9 280X in terms of mining. I managed to get my hands on a few Sapphire 280X cards this past week, and have done a little bit of experimenting.

I’ll get around to updating my guide for the 280X at some point in the next couple weeks, but if you’re looking for a good starting point as far as cgminer and undervolting settings go, read on.

Undervolting and Power Consumption

First, the 280X is essentially a re-branded 7970, which means they can be undervolted using VBE7 and the method I previously outlined for the 7950. My Sapphire cards run completely stable at 1137 mV, so if you’re following my undervolting guide, simply use 1137 in place of the 1081 that I recommended for the 7950. I’ll test lower voltages at some point soon, but the 7970/280X doesn’t have a stellar reputation as  far as undervolting goes, so I wouldn’t expect too much more.

Running at 1137 mV, you can expect a 3 GPU rig to use between 850-900 watts at the wall, assuming you’re using the rest of the hardware that I recommend in my 7950 guide. You will, of course, need to upgrade the power supply to something a bit larger to accommodate the 280X’s larger power draw—I recommend a 1000+ watt gold or platinum rated PSU. The best choice for those of you without access to very cheap electricity is probably something like this platinum-rated Seasonic PSU. This gold-rated Corsair is a bit less expensive and also a good choice. If you’re looking to run four GPUs, this eVGA PSU has enough PCIe connectors without dealing with splitters.

Cgminer Settings and Performance

These are early test results, but they should get most of you up and running with acceptable performance. My tests were done on a platform with all of the hardware outlined in my guide, the only exception being that the PSU was substituted for a larger 1000 watt unit, and of course the 7950 GPUs were replaced with 280X cards.

For my tests, I was running Xubuntu 12.04 with the latest beta AMD Catalyst drivers installed, AMD SDK 2.7, and cgminer 3.7.2. I’m also using a 280X-optimized scrypt kernal in cgminer. I’ll be looking at Xubuntu 13.x and other driver versions (and Windows, too!) in the coming weeks.

The best results I saw were with the following cgminer settings:

-I 13 -g 2 -w 256 --lookup-gap 2 --thread-concurrency 8192 --gpu-engine 1000 --gpu-memclock 1500 --temp-target 70 --auto-fan

This gets me roughly 710 Kh/sec per GPU, completely stable. Oddly enough, setting the core clock speed any higher than 1000 mhz results in lower cgminer performance.

I’ve read about some people getting speeds up to 750 Kh/sec with other brands and/or other configurations, but in my limited testing that was the best that I was able to achieve without compromising stability.

If you have another brand of 280X, you may want to try 1080 mhz or 1060 mhz for the core clock speed (--gpu-engine 1080), as many people report the best success in that range.

One interesting note is that the 280X seems to be pretty sensitive to heat, and will self-throttle its performance down whenever GPU temperatures get over 70C or so (at least, my Sapphires do). Setting cgminer’s auto-fan temp at 70C  prevents this, although I run my rigs in a fairly cold room—some of you may need to point a box fan at your rigs to get the best performance out of your 280Xs.

I’ll be trying to get my hands on other brands of 280X cards, especially the ones by Gigabyte and MSI (although many are reporting good results with the Asus and PowerColor models, too)—although I’m sure most of you have noticed that they’re fairly difficult to come by right now.

If you’re currently running a 280X-based rig, please feel free to leave a comment below with your settings and results!