Perhaps you should consider doing parallel mysqldumps of databases or individual tables.
I explained how to do this back on April 17, 2011 : How can I optimize a mysqldump of a large database?
Don't worry about trying to set the options for foreign_key_checks because the header of a standard mysqldump contains directives to set such things :
-- MySQL dump 10.13 Distrib 5.5.23, for Linux (x86_64)
--
-- Host: localhost Database: zm3_quizzes
-- ------------------------------------------------------
-- Server version 5.5.23-55
/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;
/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
/*!40103 SET TIME_ZONE='+00:00' */;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
It would be simpler for you to add the following to /etc/my.cnf
[mysqldump]
max_allowed_packet=1G