Restoring and snapshots

David Christensen dpchrist at
Sun Apr 12 08:23:12 UTC 2020

On 2020-04-11 22:19, Andrea Venturoli wrote:
> On 2020-04-12 00:18, David Christensen wrote:
>> I am confused:
>> *  What is the type of the filesystem that was the source of the backup?
> ZFS in the example above, but I've got the same problem with UFS, as I 
> also use snapshot there.

>> *  What tool(s) did you use to backup?
> Sometimes Bacula, sometimes some custom scripts.

>> *  What is the type of the filesystem that was the destination of the 
>> backup? 
> Could be UFS, bacula volumes, tapes, ZIPs, etc...

>> *  What tool(s) are you using to restore?
> Again either Bacula or some custom scripts.

>> *  What is the type of the filesystem that is the destination of the 
>> restore?
> Usually UFS or ZFS; could be something else.

>> So, the backup source filesystem and the restore destination 
>> filesystems are both ZFS (?).
> Possibly, but not always.

>> The upper Unix filesystem path should be an empty directory.
> Should, but not always is.
> Sometimes I found "forgotten" files in the directory which is the target 
> of the nullfs mount. Of course those files are usually hidden and 
> probably useless, but must be taken into account.

I would do the housekeeping -- unmount the filesystems that are 
overlaying the mount point directories containing forgotten files and 
move the forgotten files to wherever they belong, or delete them.  There 
is nothing you can do about the copies that have already been 
snapshotted (other than destroying those snapshots).

>> I believe it is a result of the 'mountpoint' properties of the two ZFS 
>> file systems and how ZFS represents filesystem snapshots in the Unix 
>> file system.
> No, this can happen with UFS too.

It sounds like you are using file- and directory-level backup tools for 
ZFS filesystems (?).  I did that for a while and it works, but I knew I 
was doing it the wrong way.

If you are using file- and directory-level backup tools to back up ZFS 
snapshots, that definitely sounds like you are barking up the wrong 
tree.  That is what ZFS replication is for.

Now I'm using ZFS snapshots and replication to backup ZFS filesystems to 
other ZFS pools.  I still use rsync to backup non-ZFS filesystems, but 
the backup destinations are ZFS filesystems; which are fed into 
zfs-auto-snapshot and the rest of my backup processes.  My tar/gzip 
archives are now sourced from ZFS snapshots rather than live 
filesystems.  Life is good.  :-)


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