2011

Sat, Apr 30

<14:17 EEST> Doing my share of May Day's obligatory celebrations, I went to the school yesterday to play a small gig. It was also a nice chance to catch up with colleagues and students, and naturally to dress up in an outrageous way. In the evening I did my share of experiencing drunken stupor, by watching the movie The Hangover.

Continuing from last time's musings on GPU cooling, my rig is now complete with another HD5870, as a Gigabyte GV-R587OC-1GD arrived yesterday morning. I had high expectations for its dual-fan cooler that takes a step away from stock windtunnels towards aftermarket designs, but in practice it is not really that great.

Initially, I ran into problems as the fan did not automatically spin up with increased temperatures. Fortunately, aticonfig also allows manual fan control. The system is stable at 81-85 °C at the minimum frequency cap of 600 MHz, while the fan is set at 60%. Noise-wise it is considerably better than most stock coolers, being tolerable in a living-room corner at this speed, but the temperature is a little worrying. The default frequency cap of 870 MHz is impossible to keep under full load, lest the card throttles and/or crashes.

In a closer look, the actual heatsink is no bigger than those in windtunnel designs. The airflow pattern is also close to these longitudinal designs, with the associated problems discussed earlier.

One good thing about the heatsink is the open design, where it is easy to remove the shroud-fan assembly and try out other fans. Unfortunately, the result is not much better. There are too many inherent limitations in the heatsink, for example the standard number of four heatpipes. I guess I need to order another Shaman to get the full power of this card, with less noise and cooler temperatures.

Wed, Apr 6

<18:46 EEST> My 8-month teaching run at Viitaniemi is over as of April 1st, and tomorrow I am going back for one more time of two lessons. It looks like I may be getting more of these brief substitute jobs in the future, but generally speaking it is already the beginning of a long summer holiday :)

The latest hardware upgrade in my Bitcoin mining rig is a Thermalright Shaman GPU cooler, which does deserve a little praise. The Sapphire Radeon HD5870 has gone from howling at 87 °C to What? Are you sure the fan is on? at 52 °C. Running full load at 900 MHz, which is the highest setting without any BIOS modifications, only using aticonfig. With full 12-volt fan speed, the temperature goes down to 46, but the quieter 7-volt hookup is still disturbingly cool for GPUs that are happy to run around 80 °C for extended periods.

Of course, my other Radeons are not too hot either. Both HD5570 and HD5770 are around 60 °C with minimal fanning, as they are designed for passive cooling with huge heatsinks. Makes you wonder why most of the stock coolers are so incredibly bad, both for CPUs and GPUs. Cost is hardly a dealbreaker, since the stock coolers already have plenty of heat piping, fins and fans. However, there is a general difference in design:

Stock GPU cooler:

Fan -> ############################################ ->
Fan -> ############################################ ->

Aftermarket cooler:

Ffffffffffffaaaaaaaaaaaaaaannnnnnnnnnnnnnnn
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |
V  V  V  V  V  V  V  V  V  V  V  V  V  V  V

###########################################
###########################################

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |
V  V  V  V  V  V  V  V  V  V  V  V  V  V  V

The volume/area of the heatsink is the same in both cases. In the stock cooler, only one end of the heatsink gets cool air, and the rest will have to try and cool down using progressively warmer air. To maintain a temperature differential, the chip must get quite hot. Whereas in the aftermarket cooler, the entire heatsink gets cool air. Also, when you consider a similar flux of air (volume/time), the stock cooler needs a much higher velocity. This means more noise, and not just from the fan.

On the other hand, as I have mentioned earlier, the stock 'windtunnel' design is great at getting air out of the case (if you use one). The aftermarket cooler also takes up more space, and a Shamanized GPU takes a total of 4 slots. But who's counting when you want it cool and quiet?

In fact, the Shaman could probably use pure convection, with a little underclocking and some ductwork. However, it turns out that the hottest parts of the graphics card are elsewhere, at the power regulation section, so overall it does need some fanning.