Recently realized in my farm that my 470 4Gb rigs, which were all 6 card setups at the time, were not generating the dag any longer for ETC and then soon after ETH dag approached whatever level it was that pushed my system over the limit. After a day of wondering what to do, I realized a 470 rig I have with 1 8Gb 580 in it was working fine with the other 5 cards being 470 4Gbs. I took apart one of my 580 8Gb rigs and replaced a card on one of the 470 rigs. Mined perfectly fine. Did this to the whole farm and split the gpus essentially so every 4Gb rig has atleast 1 8Gb card in it. As for now this works no issues. I have a p104-100 rig with 1 470 4Gb in it and same thing, generated dag and mines.
I tested this on 2Gb R7 200 gpus and works perfectly fine. Card generates the dag as long as the system has one available card that is able to fit the dag on it. This is identical to how the 470 rigs are operating.
The same goes for 470 4Gbs with rx 5700s and the same with the R7 200s with the rx 5700s.
It sounds like 4GB isn't enough for the DAG since the current DAG is 3.27GB for ETH or 3.34GB for ETC.
RedPandaMining recently posted a video on his Youtube Channel.
https://www.youtube.com/watch?v=xRIX5mpVntk
It would be awesome if it worked on 3gb Nvidia cards, but from what I have seen its only a fix for AMD cards with 4gb and below running on windows. I setup a windows box with a GTX 1070 and a couple gtx 3gb 1060s with no luck, then I tried a mixed mode setup with an 8gb AMD card as the main GPU with no luck as well. I figured it would not work with Nvidia cards below 3 gb, but I wanted to try it out for kicks. If anyone else tried and had luck let me know.