Hello. Next time please take the photo of the smoke exiting the smoker. That smoke "looks" on the blue side so "maybe" not bad. I assume you are new to smoking so I don't want to confuse you but white smoke is not "NECESSARILY" a bad thing. You need to learn to control your smoker so that you can achieve thin blue smoke but it also depends on what you are trying to do. If you are trying to smoke a large chunk of meat for a long period, you want thin blue smoke. If you are grilling a couple 1" thick ribeyes; get the coals white hot, throw on some wood chips add the steaks and let the white smoke roll. 3-5 minutes one side and 3-5 minutes other side and off. My rule of thumb is IF I can cook it in 1 hr. or less I don't worry about white smoke. Some folks will say 2 hours but I stick to my rule. I also smoke at a bit higher temp with some foods. I figure I can smoke a chicken in 1 hour at about 300- 325. NOW! IF you want MORE smoke flavour, slow it down. Just my opinion. Keep Smokin!
Hard to tell, but that looks quite thick smoke and more white to me. Just smoke for an hour to be on the safe side I'd say. If the wood isn't on fire I'd imagine white smoke is what you have. Maybe creeping into blue.
I don't see why size of the wood matters. Smaller pcs might catch faster and smoke. Larger pcs might take longer to start smoking. I've used big chunks before and chips. The bigger chunks just took a little longer to start smoking. While the chips start smoking a lot faster. My guess is surface area of wood on heating element. That is if its a MES style unit. In bigger units people throw in big logs all the time with no problems. In eletric units. Your restricted by the opening at the loader and if you have rods just above the tray that would cause it not to make contact with the tray. I've switched over the AMAZEN and never been happier with using pellets. But I still use wood chunks and chips once in a while.
What constitutes a "large" piece of wood is relative: throw a 30 pound, eight-inch dia. log on top of a lit candle and a blazing log-on-fire will not ensue. The result will be a long-smoldering acrid white smoke. Throw that same log into a good sized offset that already has about 30 pounds of coals going and it will become an inferno in no time, producing the desired sweet smoke. Chips, chunks, splits, logs, and trees can all be the source of pleasant tasting barbecue, or of ruined meat with more of an ashtray flavor. It's a matter of proportion of added fuel to existing combustion.