My understanding is that that parameter understands --devices AMD and --devices NVIDIA. I have AMD only. I need to mine ETH with 3 8GB cards and BEAM with the remaining 4GB cards.
In addition to the above if I run twice lolminer with two different strings how can it work? I mean how is the JSON and config file going to be?
It understand --devices AMD and --devices Nvidia or alternatively you can use --devices 0,1,2,4 to skip e.g. 4th card (index 3) in the system.
So you can indeed open two miner windows where one is pointed to Ethash and one to Beam, both using just different devices strings.
In json the configuration is 100% same
"DEVICES" : "0,1,2",
will select first 3 cards,
"DEVICES" : "3,4,5",
will select the 2nd set.