ok, seems like I'll need to use a dremel tool.

Now the question is power: I'm already using a cpu->pci and 2x molex -> pci.

I have only 2 more molex connectors on the PSU (which has plenty of watts -- 1250)

Do any of these have a chance of working, and which is likely to be better:

1. Split one of the pci connectors
2. Supply half of each of two molex->pcie adapters from a single molex line, using these adapters in two different gpus
3. Split the CPU line (cpu is a sempron 145, and I'm running headless so cpu usage is around 5%. so draw on the cpu line should be pretty low currently)

Will the 1x extender fit underneath a GPU? For example my rig uses an MSI 790 gd70, with 4 gpus. I'd like to add a fifth using the pci 1x slot, but I'm not sure if I'll need to also extend the gpu that covers that slot.

Check your cpu usage. Is it pegged? Also, does the primary display run by itself get a steady hash rate as high as the secondary card run by itself?

There is some kind of issue with the ubuntu gui that causes cpu to max out when mining on the primary display, slowing down ALL gpus.

If you switch to headless it will go away.

Cpu usage should be < 10% if things are working properly.

seems to be a bug in linux with the graphics drivers & gnome or whatever the desktop gui is called.

Here's how it affected me:

running 4 cards. If I ran the 3 that my monitor was not plugged into, all was fine.

If I ran the "main" card, cpu would peg at 100%. The mhash rate of ALL cards would fluctuate wildly, averaging about 10-15% lower than when not running the main card.

Top would show kworker using 40%cpu, and the miners (phoenix) using up to 20%

I switched to headless ( with a /etc/init/gdm.conf that looks like exec /usr/bin/X 2>&1) and all was good.

all four cards run at a consistent rate, and cpu is about 5%


(this is actually the first time in my life I've used a linux gui! even though I've logged thousands of hours on linux servers. And I didn't use it long before ditching it...)

4 X 6870s stay cool enough if you have a side fan. I'm using a coolermaster haf x, it has a large side fan. Can't run all four cards overclocked without the side panel on, but with it on I stay below 70C.

They are noisy though.

Also, they won't all go to 1000

And some of them need to be kept really cool to be overclocked, like under 70.

Don't forget you will need adapters, molex to pcie and/or cpu to pcie, because the cards require two pcie lines each, and power supplies will have only 6

I deliberately bought a really good power supply because it was on sale and I intend to use it somewhere else later. But even that had only 6 pcie connectors. Maybe there are psus with 8, but I don't know any.

I bought 6870s because at the time, in Vancouver with ncix sale, they were definitely the best mhash/$. Currently 6950 is slightly better. IF you buy them separately so you get rebate on each -- buy them all at once and you only get one rebate!