More work on the hashing supercomputer.
I’ve been transforming my NAS box into a hash-cracking station. I acquired a Gigabyte HD 6770 SC, a high performance, high frequency AMD GPU that’s OpenCL friendly. This card is cheap (and quiet) for its computational power because it has less RAM than competing graphics cards in the same bracket (graphics RAM speed matters for this application, but capacity has minimal impact).
For comparison, here’s the Gigabyte HD GV-R797D5-3GD-B. One of the most hard-core graphics cards available when this was written.
| Aspect | 6770 | GV-R797D5-3GD-B | % inc. | Relevance |
|---|---|---|---|---|
| Price | $139.00 | $793.00 | +471% | 6770 is near the sweet spot |
| Core Clock | 850 MHz | 925 MHz | +9% | We care about this |
| Memory Clock | 4800 MHz | 5500 MHz | +15% | This too |
| Memory Size | 1024 MB | 3072 MB | +200% | This can be flexible |
For basic OpenCL based number crunching, the 6770 has some pretty decent specs for the price.
Well, today was a hot one in Melbourne and after testing out the card with OCLHashCat the rig nearly melted, reaching a GPU temperature of 90°C.
There are reports of these cards running hot. The fanless design may account for that, and they probably had to accept certain trade-offs when designing the thing. The weird thing was, just replacing the factory thermal grease with some Arctic Silver 5 dropped the idle temperature from 65°C to 52°.
I’ve moved from 2 to 4 silent fans for good measure, taking the full-load temperature (92% GPU utilization for 30 minutes) down to a stable 71°, and idle temperature down to 43°.
Here’s the Pyrit benchmark of the continuously achievable WPA2 hash-rate (4,096 iterations of HMAC-SHA1 per WPA2 PMK).
Around one hundred million HMAC-SHA1s per second (leveraging SSE2 on the 2.4GHz Athlon II does about 2% of that). Nice.
BitCoin Mining Test
Using poclbm with the DeepBit minding pool. This low-cost experiment rig achieves around 120 MH/s.
UPDATE 2012/01/17:
Using cgminer with OzCoin increases that to 168.1 MH/s steady.
Hardware shots
The HD 6770 SC: 
Heatsink removed: 
The card that hides underneath: 
Re-installed with two extra fans (airflow from bottom to top): 