Using Rsynch to Backup Directories

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Intro - 

We want to backup files on a given volume.
Ideally, we'd have multiple backups of the file at different stages of development.

Traditionally, you'd use tar to make an archive on another volume.
Then, each day we'd run an incremental backup and add an addendum to the archive.

However, with rsynch we can do a much neater trick.  
We maintain directory trees for each time (eg. LAST_WEEK, 2_WEEKS, 3_WEEKS)
which just consist of links.
Each weeks we shift the links.
		3_WEEKS is deleted.
		2_WEEKS -> 3_WEEKS
		LAST_WEEK -> 2_WEEKS
		LAST_WEEK = rsynch copy of source.
If a source file (eg. FILEA) matches 2_WEEKS/FILEA then LAST_WEEK/FILEA is just a link
to the same physical file as 2_WEEKS/FILEA.
If the source file has changed, then version two of FILEA is copied to the backup volume.
LAST_WEEK/FILEA linsk to version 2.  2_WEEKS/FILEA links to version 1.

This is described more fully in rsynch_backup.html

	crucial commands are,
	cp -al  (archive and link)
	rsync -av --delete --exclude-from=$FILE_LIST / /$Rsynch_Path/current  

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Implimentation 

Tried this out backing up my home directory on BIGBRO II.
Goal - Keep hourly, daily, weekly and monthly backups.

Scripts are in /usr/local/sbin
  Each backup type done by - 
		hourly_backup
		daily_backup
		weekly_backup 
		monthly_backup
  Files to backup specified by 
		backup_list
  Files written to /mnt/hdb/backup
		current
		hourly1 -> 1 to 2 hours old
		hourly2 -> 2 to 3 hours old
		hourly3 -> 3 to 4 hours old
		daily1 -> 0 to 1 days old
		daily2 -> 1 to 2 days old
		weekly1, weekly2
		monthly1, monthly2 - 1 to 2 months old			
  Scripts are symbolically linked to 
		/etc/cron.hourly
		/etc/cron.daily
		/etc/cron.weekly
		/etc/cron.monthly
  Each script logs to /var/log/backup
		monthly_date
		weekly_date
		daily_date
		hourly_date
		hourly_error --> errors in maintaing main links.
		hourly -> report on copying backup archive.	 					


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Shifting directory trees around.

Consider weekly_backup.  The main part is at the end where we,

	rm -rf weekly2
	mv weekly1 weekly2
	cp -al current weekly1
	
Hourly is different in that it uses,
	rsync -av --delete --exclude-from=$FILE_LIST / /$Rsynch_Path/current
to generate the current folder.

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Selecting files to backup.

We use the --exclude-from option for this.  In the present example we back up
	/home/toombes but exclude the sub-trees /home/toombes/bigsis and /home/toombes/bigbro
as these are mounts to other machines.

Our exclude file, (backup_list) works like this
	- /home/toombes/bigbro
	- /home/toombes/bigsis   # Ditch the two mounts
	+ /home			 # Descend into /home
	+ /home/toombes		 # Descend into /home/toombes
	+ /home/toombes/**	 # Descend into all subdirectories of /home/toombes
	- *			 # Ditch if it doesn't match this pattern.

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References
	rsynch_backups.html by Mike Rubel
	http://samba.anu.edu.au/rsync/