Questions with rsync

[GMS S]

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Here's my full-system rsync backup script. It goes to an external USB drive.

#! /bin/sh
cd /media/MyBookLX/sds-desk
rm -fr backup.9
mv backup.8 backup.9
mv backup.7 backup.8
mv backup.6 backup.7
mv backup.5 backup.6
mv backup.4 backup.5
mv backup.3 backup.4
mv backup.2 backup.3
mv backup.1 backup.2
cp -al backup backup.1

touch /last_backup_ts
rsync -va --exclude-from /usr/local/bin/do-backup-excludes --delete /
/media/MyBookLX/sds-desk/backup/

The exclude list is

/home/*/.gvfs/
/home/*/.google/
/home/*/.dbus/
/home/*/.fonts/
/proc
/tmp
/var/tmp
/media
/sys
/dev

- --

  Steve
]

There are so many backup.1,backup.2,backup.3 ... files.Why?
How did these files come?
Did you create these 9 files in the external USB?