I've been running the following setup fine for the past week.
Sapphire Tri-X 290
Asrock 970 Extreme4 Mobo
Xubuntu 13.10 (with 13.12 AMD drivers)
Sgminer 4.1
1000W PSU
I just added a DIAMOND R9 280X 3GB.
It is recognized, but when I run sgminer, it's like it's throttled, only getting 40-90Kh/s. The odd thing, if I disable the Sapphire (GPU0), the DIAMOND (GPU1) picks up to it's expected hash rate (around 700). It's as if something doesn't want both of my cards running at full load. I don't think I need a dummy plug, but I do have one plugged in but it doesn't effect anything.
https://i.imgur.com/hQXhLoA.pnghttps://i.imgur.com/2Pw5z0j.pngsgminer -o stratum+tcp://useast.wafflepool.com:3333 -u <user> -p xp --failover-only -o stratum+tcp://uswest.wafflepool.com:3333 -u <user> -p xp -I 20,13 -g 1,2 -w 256,256 --thread-concurrency 25601,8192 --gpu-memclock 1499,1499 --gpu-engine 1040,1000 --lookup-gap 2,2 --auto-fan
Any help is much appreciated.