差分备份可能会备份增量备份忽略的数据，但是差分备份恢复速度要比增量快，因为它仅仅需要上一次完全备份和最近的一次差分备份；而增量备份则需要从上次完全备份及以来的每一次增量备份。
为了使用者写方法进行备份，需要使用tar命令的－N或--newer选项，后面跟一个时间，时间应该是通常的日历格式(例如：03/12/199 = March 12th, 1999)。
tar -cvf /dev/st0 --newer 03/12/1999 /
该命令将备份系统中所有在March 12th, 1999及其以后被修改的文件。
我下面提供了一个简单的脚本文件来作为一个同时实现完全和差分备份的自动化模型。在使用该脚本以前，请注意检查脚本头定义的环境变量以满足自己的需要。
#!/bin/sh
#
#######################################
#
# TAR backup script to cover daily and weekly backups on one tape.
# Generic UNIX version - edit variables as required
#
# For this to work, it MUST be started on a Monday!
#
# Copyright (c) 1999, Tim Jones
# Permission granted for use/modification
#
# Tim Jones/Linux Magazine provide this shell script with no warranty
# (implied or otherwise)
#
########################################
DOW=`date +%w`
DATE=`date +%D`
DAY=`date +%A`
DEVICE="MY REWIND TAPE" # Rewinding tape drive
NDEVICE="MY NO_REWIND TAPE" # non-rewinding tape drive
REWIND="mt -f $DEVICE rewind"
EOD="mt -f $NDEVICE eod"
FSF="mt -f $NDEVICE fsf"
MAILLIST="root" # list of users to receive backup notice
if [ $DOW = "6" ]
then
# This is Saturday, so append and write the whole system!
$EOD
echo $DATE > /tmp/.LASTFULL
tar -cvvf $NDEVICE / >/tmp/backup.txt
$REWIND
$FSF 5
tar -dvf $NDEVICE >> /tmp/backup.txt
$REWIND
cp /tmp/.LASTFULL /etc/.LASTFULL
else
# this is not Saturday
case $DOW in
0)
# it's Sunday - nothing to do
exit 0
;;
1)
# Monday, Let the tape rewind for the difference verification
echo $DATE > /tmp/.LASTINC
tar -cvvf $DEVICE --newer `cat /etc/.LASTFULL` / >/tmp/backup.txt
cp /tmp/.LASTINC /etc/.LASTINC
;;
*)
# Other Days, must rewind manually and Inspect, -i
$EOD
echo $DATE >/tmp/.LASTINC
tar -cvvf $NDEVICE --newer `cat /etc/.LASTINC` / >/tmp/backup
$REWIND
$FSF `expr $DOW - 1`
echo "************ Verifying ${DAY}'s backup" >> /tmp/backup.txt
tar --dvf $NDEVICE >> /tmp/backup.txt
cp /tmp/.LASTINC /etc/.LASTINC
$REWIND
esac
fi
mail $MAILLIST < /tmp/backup.txt
rm -f /tmp/backup.txt
# END OF SCRIPT
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