Re: [List] Re: Backup/restore recipe

On 12/11/2025 19:06, Eugene R wrote:
>
> Hello and thanks to everyone for the suggestions.
>
> Overall, making backups is indeed pretty straightforward using ZFS or 
> an assortment of "agnostic" filetree-based backup solutions. And in 
> the latter case, selective restore is also easy.
>
> What I do not understand is how should one approach restore in 
> scenarios 2 and 3 (and how to stage the backups for them).
>
>     - selective restore of specific files or subtrees to a working
>     FreeBSD system (this one is reasonably obvious)
>     - (essentially) exact duplicate of the original system state on
>     the same or different machine (ideally binary exact if hardware
>     allows, i.e., an equivalent of a cloned server snapshot)
>     - functionally equivalent duplicate (i.e., the same filesystem
>     content over the potentially different low-level layouts)
>     In cases 2 and 3, we likely will have to start from a clean
>     machine, possibly with dummy Linux or FreeBSD installation.
>
> Eugene
>
Using ZFS send to replicate the datasets does indeed produce a "binary 
exact" snapshot for most intents. The blocks might be stored in 
difference places on the destination but to the rest of the system it's 
identical. You can copy the datasets onto a pool on a new drive, copy 
the bootloader on to it, plug it into a server and just boot it back up. 
If you're replicating the datasets to their own pool. on [a] dedicated 
drive[s]  you can maintain a ready-to-go clone of the live server.

You can also go into the backup datasets and copy individual files (or 
whole datasets) out as required. Make sure the backup datasets are set 
to "read-only" or the act of accessing them

I've seen suggestions for various file level backups, which have their 
place, but you specifically asked to backup the whole running system. If 
you replicate a ZFS snapshot you get everything in a way that's not 
possible when copying individual files from a live system. AIX has this 
facility in JFS2, but it's not common.

If course, if it's a VM you can take a snapshot of the VMDK and copy 
that, but it's not actually as good as a ZFS snaphshot guarantees the FS 
is in a consistent state whereas VMWare has no way of telling if it's 
mid-way through a TXG. But I use real hardware :-)

Regards, Frank.