On Saturday, 3 February 2024 17:32:17 GMT Rich Freeman wrote:
> On Fri, Feb 2, 2024 at 6:39 PM Grant Edwards <grant.b.edwards@gmail.com> 
wrote:
> > On 2024-01-31, Rich Freeman <rich0@gentoo.org> wrote:
> > > In any case, these COW filesystems, much like git, store data in a
> > > way that makes it very efficient to diff two snapshots and back up
> > > only the data that has changed. [...]
> > 
> > In order to take advantage of this, I assume that the backup
> > destination and source both have to be ZFS?
> 
> So, the data needs to be RESTORED to ZFS for this to work.  However,
> the zfs send command serializes the data and so you can just store it
> in files.  Those files can only be read back into zfs.
> 
> It is probably a bit more typical to just pipe the send command into
> zfs receive (often over ssh) so that you're just directly mirroring
> the filesystem, and not storing the intermediate data.
> 
> > Do backup source and
> > destination need to be in the same filesystem? Or volume? Or Pool?
> 
> No on all of these, but they can be.
> 
> > If you'll forgive the analogy, we'll say the the functionality of
> > rsync (as used by rsnapshot) is built-in to ZFS. Is there an
> > application that does with ZFS snapshots what the rsnapshot
> > application itself does with rsync?
> 
> There are a few wrappers around zfs send.  I'm using
> sys-fs/zfs-auto-snapshot and what looks like a much older version of:
> https://github.com/psy0rz/zfs_autobackup
> 
> > I googled for ZFS backup applications, but didn't find anything that
> > seemed to be widespread and "supported" the way that rsnapshot is.
> 
> They're less popular since many just DIY them, but honestly I think
> the wrapper is a nicer solution.  It will rotate backups, make sure
> that snapshots aren't needed before deleting them, and so on.  In
> order to do an incremental backup the source/destination systems need
> to have matching snapshots to base them on, so that is important if
> backups are sporadic.  If you're just saving all the send streams then
> knowing which ones are obsolete is also important, unless you want to
> have points in time.

This article offers some comparison tests between ZFS, Btrfs and mdadm+dm-
integrity.  Although the setup and scenarios are not directly comparable with 
the OP's use case they provide some insight on more typical implementations 
where these fs excel.

https://unixsheikh.com/articles/battle-testing-zfs-btrfs-and-mdadm-dm.html