Note: Brussels sprouts are sometimes sold in 10-ounce containers, so you can use three containers for 30 ounces of sprouts, if you wish, instead of the full 2 pounds.
Preheat the oven to 400ºF.
Cook the pancetta and 2 teaspoons of oil together in a large skillet over medium heat, stirring occasionally, until the pancetta is lightly browned, about 8 minutes. Using a slotted spoon, transfer the pancetta to paper towels to drain.
Toss the Brussels sprouts and the remaining 2 tablespoons oil in a large bowl. Spread on a large rimmed baking sheet. Bake, stirring occasionally, until browned and just tender when pierced with the tip of a small sharp knife, 20 to 30 minutes. During the last few minutes, stir in the reserved pancetta. Transfer to a serving bowl.
Whisk the balsamic vinegar and brown sugar together in a small bowl. Drizzle over the Brussels sprouts mixture, season with salt and pepper, and toss gently. Add the raspberries and toss again. Serve hot.