Backup newly modified files
My server backups over 20GB files everyday. It takes hours to tar those huge amount of files. I think this kind of stupid task is harmful to hard driver. One more stupid issue is that over 99% of files are not modified since last backup. So, here is the command to let me backup newly modified files only.
tar -zcvf /save/to/file.tar /filePath/* –newer-mtime ‘1 days ago’
You may want to change “1 days ago” to 2 days, or 5 days.
By the way, it’s better to do full backup monthly or bi-monthly. 
Why not just use rsync?
Thats what I use for backups.
I just have a daily script to backup to another machine, and a monthly script to backup everything again to another box just in case.
Works well for me
You are right, Lawrence.
I have make a rsync post for people who looking for an alternative backup method.
http://www.fengcool.com/2009/07/rsync_server_and_client_backup_server_file/