tar to create a snapshot of different parts of the filesystem on my servers and then ftp that snapshot to an offsite location for archiving.
I would like to only start that operation when something has changed. Some of the backups run on all the system's folders that change very infrequently (i. e. when new software is installed or the configurations are modified).
Whenever a change does happen, I want a complete snapshot. I could produce a list of modified files with
find, but I really only need to know if that list's length is 0 or greater. Using find is too slow for that.
I am aware that there is incremental backups and I'm already using rsync in conjunction with ZFS for that in other situations. However, here the backup host is an FTP server (so no rsync), I need complete backups (because the backup archive is used as an image to restore or clone servers) and I want compressed output (so tar is handy).
Edit: Note that I'm not looking for incremental backup (I have that), but rather for a fast (that kinda rules out find and the like) and easy way to decide if a full snapshot would be identical to the last one. Maybe my phrasing wasn't so good. I edited the title now.