Can anyone comment on using PCI-E risers?
I just implemented a third card on a rig using a riser - and the card in the third slot that is on the riser is only getting like 350k/H - where the other 7950 in directly in slots 1/2 are getting 550k/H.
Can riser lower hashrate that much? Also the card with the riser won't let me set fan speed in cgminer?
Check if the riser is seated correctly.
I had an issue with one card showing erratic behavior (sometimes not detected on reboot, "DEAD" in cgminer at stock settings, overall lower hash rates than the other identical cards on risers) until I firmly reseated the riser.
This Litecoin mining is less a Science at this point than it seems to be Sorcery.
I had to completely and radically change the cgminer settings to get the same performance from this card on a riser in the 3rd slot.
Why on earth would two identical cards require wildly different settings in different slots on the same motherboard but in the end perform the same? I think there is a LOT better performance that could be had from GPUs in scrypt mining - this inconsistency shows unoptimized and possibly buggy software imho. (at least on RADEON 79XX).