Place the pears, sugar, vinegar, water, and salt in a heavy, 2-quart, non-reactive saucepan. Bring to a boil, lower the heat, and simmer until the relish thickens, stirring occasionally, about 20 minutes depending on the amount of juice and the ripeness of the pears.
Transfer the relish to a medium bowl and cool to lukewarm. Add the raspberries and vanilla and stir to mix well. Allow the relish to cool to room temperature, gently stirring occasionally. Cover and refrigerate until chilled. Serve cold.