Heat oven to 350 degrees F. Coat two 9 x 2-inch round cake pans with nonstick cooking spray. Line bottoms with waxed paper; coat paper with spray.
In medium-size bowl, whisk flour, baking soda, cinnamon and salt. In large bowl, with mixer on medium speed, beat sugar, oil, eggs and vanilla until blended. On low, gradually beat in flour mixture until smooth. Stir in carrots, pineapple with juice and nuts. Divide batter between prepared pans, 3-1/2 cups each; spread evenly.
Bake in 350 degree F oven 45 to 50 minutes, until wooden pick inserted in centers comes out clean. Cool cakes in pans on wire racks 10 minutes. Turn out onto wire racks; remove pans and waxed paper. Let cool completely.
In large bowl, with mixer on medium speed, beat cream cheese, butter and vanilla until light and creamy, 2 minutes. On low speed, gradually beat in confectioners sugar. Beat until fluffy, about 1 to 2 minutes (you will have about 5 cups frosting).
Measure half way up side of each cake layer; place wooden picks around sides for guide. With serrated knife, cut each cake horizontally in half; remove picks. Place one layer, cut side up, on platter. Spread 1/2 cup frosting over top. Repeat two more times with layers and frosting. Top with remaining cake layer, cut side down. Spread 1 cup frosting over top; spread remaining frosting around side.
Refrigerate at least 1 hour until frosting is set. Store, covered, in the refrigerator for up to 3 days. Makes 16 servings.