Personally I use star (streaming tar) from
http://cdrecord.berlios.de/old/private/star.html It's designed for use with tape drives and gives me dramatically quicker backups.
Here is a short script that should fill your needs. It's a highly stripped down version of what I use. Be sure to check that the directories are right for you.
#!/bin/bash
# a few constants
TarDir="/var/spool/mail"
Drive="/dev/st0"
MT="/opt/schily/bin/mt -f ${Drive}"
STAR="/opt/schily/bin/star"
OPT="-c -h -v -fifostats f=${Drive}"
DATE="/usr/bin/date"
echo "=============================================="
echo `$DATE` "start backup"
cd $TarDir
$STAR $OPT *
echo `$DATE` "taping complete"