Using a centralized backup server might be one of the most important safety nets you can implement. At some point data is going to be lost and you are going to be relieved to know the files are accessible on the backup server. But, we are not talking about a tape server with proprietary backup software where it could take hours to get the data back.
We are going to design the logic using the open source binary rsync to backup to on-line storage; using a raid or server with redundant disks to rsync the data from other servers and user systems to the backup server. Rsync is an incredible backup tool.
Rsync is one of the most powerful open source tools you can use. It allows you to specify a list of files or a directory structure and make an exact copy to another location. What is different in rsync, than copy for example, is it will only copy the data that is different from the source and target locations.
If you have 100 gigs of data you need to backup, but only 4 gig has changed since the last copy you made, there is no need to copy over the whole 100 gigs again. Doing so would waste your time and put a strain on network bandwidth. You also do not want to go through the files manually using "find" and figure out what changed. This is where rsync comes in. You can set up rsync to mirror a list of directories and/or files and compare that list against the target location where you want the files to be backed up. The efficiency of rsync comes from the method used to backup the data.
When data is added or deleted from a file the entire file does not change, only part of it does. Rsync recognizes this and only copies over the changed data. If you had a 100 meg file and only 1 meg changed, then only 1 meg would need to be transfered. Very efficient indeed.
With online backups you can have all of the data available online all the time. If a user deletes their own mail folder they can retrieve it themselves through any method you allow. For example, you could setup a sftp or passworded ftp server allowing your user to browse their backups and retrieve the files of their choosing. Using this ideology can save you hours of tedious backup retrieval time per week if you have "rm -rf" clumsy users
Setting up the backup file structure
Automating backups with cron
Wrapping ssh for safety and security
Read more http://blogmee.info/index.php/backup-remote-server-rsync/
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