Let eggs stand at room temperature for 30 minutes. In a large bowl, beat egg yolks. Gradually add 1 cup sugar, beating until thick and lemon-colored. Combine pecans, flour, cocoa, baking soda and salt; add to yolk mixture alternately with water. Stir in vanilla.
In another large bowl, beat egg whites until foamy. Gradually add remaining sugar, 1 tablespoon at a time, beating until stiff peaks form; fold into batter.
Spoon into two greased and floured 9-in. round baking pans. Bake at 375° for 20-22 minutes or until cake springs back when lightly touched. Cool for 10 minutes before removing from pans to wire racks to cool completely.
For frosting, in a large bowl, beat cream until soft peaks form. Beat in confectioners' sugar, cocoa and vanilla until stiff peaks form. Cut each cake horizontally into two layers. Place bottom layer on a serving plate; top with about 1 cup frosting. Repeat layers twice. Top with remaining layer.
For glaze, in a small saucepan, combine cocoa, water and butter. Cook and stir over medium heat until butter is melted. Remove from the heat; stir in confectioners' sugar and vanilla until smooth. Spread over top of cake. Spread remaining frosting over sides of cake. Store in the refrigerator.