*Caution: Threadjack !!!!* Backup strategies

Matthew Seaman matthew at freebsd.org
Fri Aug 28 15:21:50 UTC 2015

On 08/28/15 15:07, William A. Mahaffey III wrote:
> Warren's (fabulously lucid) page brings up a question for me. For years
> I have used a 'pull' strategy for across-the-LAN backups, w/ my 'backup
> servers' using tar or rsync to access data for backup on NFS-mounted (or
> automounted) directories that I want backed up. This all happens
> automatically overnight under cron. I am usually *not* backing up system
> files, but rather user data, although I have recently started backing up
> system stuff as well. Warren's page consistently illustrates a 'push'-ed
> backup, & involves system files. I am *dead* serious about automated
> backups, no possibility of forgetting to do it that way, but I always
> thought that trying to backup 'live' system files was a bad idea
> (right/wrong ?). There doesn't seem to be a way to do a 'push' backup
> w/o messing with live system files. I guess I am asking about 'best
> practices' for backups, & the wisdom/validity of backing up 'live'
> system files. Sorry for rambling, but the question(s) popped up for me
> while reading Warren's web page. Any input appreciated. Have a nice day
> & weekend :-).

Push vs pull strategies are a matter of taste.  With a pull strategy,
almost all the configuration is in one place and the backup server can
control resource usage -- so it's preferable if you've got a large
number of machines to back up.  Push is usually a bit simpler to script,
plus it's the only viable way of backing up to eg. a cloud service.

True, you cannot guarantee a coherent backup from a live filesystem.
Your choices are either to unmount the filesystem (or otherwise render
it quiescent) or else use some form of snap-shotting.

Snapshotting is generally the preferable option, since it avoids
disrupting the system too much while the backup is happening.  The
built-in native backup mechanisms support this: for UFS, dump(8) has the
-L flag (except with soft-updates+journalling), and for ZFS, zfs send
only works on snapshots.

Of course you can always create snapshots manually, mount them somewhere
and then use whatever tools of your choice to backup the snapshot.  This
is how I use tarsnap(1).



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