I just started playing around with two 5870, but I am having stability issues. I first installed Ubuntu 10.04 LTS and followed the instructions here
to install the drivers and the miners. But the system was not stable, it would freeze randomly with some tame overclocking configuration (temperature was always under 70 degrees, usually around 55-65). So I installed Ubuntu 11.04 thinking that maybe the "old" sotware of the LTS was causing problems with the drivers. I am having the same exact problems.
I am using phoenix with the Phatk kernel and overcloaking the 5870's to 1000:1000 (gpu speed:memory speed) and the temperature never goes over 70, staying around 55-65. Curiously I get the freezes if I set the memory speed under 1000. I get 424 Mhash/s.
Also, I have tried to overclock the gpu over 1000, even trying 1025. One works fine and I get over 430 Mhash/s, temperature is fine, but when I launch the second one (also at 1025) the whole system freezes and I need to reboot. Its not one card since I have tried in the inverse order and the result is the same. Both cards alone do 1025 fine, but when the second starts the systme freezes. My rig is using a single core AMD cpu, can that be a problem because is not able to handle both gpu's? Does adding more cards will create problems for this cpu or is cpu power not an issue for mining with the gpu's?
Im guessing that the 5870 can go over 1000 Mhz because the temperature is fine. Any advice on what to do or test?
PS: I am using Phatk because I read its the quicker, but I have also read that Hashkill is very good on linux. Any comments?