BACKUP FILES SYSTEM

It seems to me that rsync backup of the OS can only be used for recovery if you can boot up the OS and run rsync. If the OS still boots, you can of course restore with rsync (or just copying files back). But if it is bricked you would need to do a full factory reset anyway.

Popping in a cloned disk on the other hand would always work, but the disk includes the data partition and not just the system. If you are using raid, then of course that data partition will then be out of sync with the full array - forcing you to restore your data from backup. That would probably work out better with flexraid (e.g. with flexraid you can keep your data off of disk 1).

Perhaps the best strategy is to maintain a shadow copy of the OS on the c volume, so you can recover files you have accidentally deleted (assuming the system still boots). And ensure you keep your backups up to date. If you are doing a lot of development, the safest way is to have a separate test system. With OS6 you can use a VM for that, but AFAIK that is not available for 4.2.x

Thanks Stephen for your exhaustive answer.
I've just installed the Rsnapshot super-poussin's addon. Initially I would like to use it to locally backup important file like php.ini, httpd.conf, to dump automatically my databases,...so in case I would have updated files that can be restored. If I managed to do that I will try for a remote backup on my Desktop PC ( this involve permissions to be set on Windows 7 folder).
I did a 'search' on the forum 'addons' section and I wonder to find no post about that addon....

Once you have a local backup on the data volume, you can use Frontview to migrate that to the PC - no need for an add-on. You do need to have permissions and sharing set up on the PC.

Though if you are developing on the PC, you can also use drag/drop to copy the data periodically.