Musings on ZFS Backup strategies

Ronald Klop ronald-freebsd8 at
Sat Mar 2 15:09:49 UTC 2013

On Fri, 01 Mar 2013 21:34:39 +0100, Daniel Eischen <deischen at>  

> On Fri, 1 Mar 2013, Ben Morrow wrote:
>> Quoth Daniel Eischen <deischen at>:
>>> Yes, we still use a couple of DLT autoloaders and have nightly
>>> incrementals and weekly fulls.  This is the problem I have with
>>> converting to ZFS.  Our typical recovery is when a user says
>>> they need a directory or set of files from a week or two ago.
>>> Using dump from tape, I can easily extract *just* the necessary
>>> files.  I don't need a second system to restore to, so that
>>> I can then extract the file.
>> As Karl said originally, you can do that with snapshots without having
>> to go to your backups at all. With the right arrangements (symlinks to
>> the .zfs/snapshot/* directories, or just setting the snapdir property to
>> 'visible') you can make it so users can do this sort of restore
>> themselves without having to go through you.
> It wasn't clear that snapshots were traversable as a normal
> directory structure.  I was thinking it was just a blob
> that you had to roll back to in order to get anything out
> of it.

That is the main benefit of snapshots. :-) You can also very easily diff  
files between them.
Mostly a lot of data is static so it does not cost a lot to keep snapshots.
There are a lot of scripts online and in ports which make a nice retention  
policy like e.g. 7 daily snaphots, 8 weekly, 12 monthly, 2 yearly. See  
below for (an incomplete list of) what I keep about my homedir at home.

> Under our current scheme, we would remove snapshots
> after the next (weekly) full zfs send (nee dump), so
> it wouldn't help unless we kept snapshots around a
> lot longer.

Why not.

> Am I correct in assuming that one could:
>    # zfs send -R snapshot | dd obs=10240 of=/dev/rst0
> to archive it to tape instead of another [system:]drive?

Yes, your are correct. The manual page about zfs send says: 'The format of  
the stream is committed. You will be able to receive your streams on  
future versions of ZFS.'


tank/home                                                 115G  65.6G   
53.6G  /home
tank/home at auto-2011-10-25_19.00.yearly                   16.3G      -   
56.8G  -
tank/home at auto-2012-06-06_22.00.yearly                   5.55G      -   
53.3G  -
tank/home at auto-2012-09-02_20.00.monthly                  2.61G      -   
49.3G  -
tank/home at auto-2012-10-15_06.00.monthly                  2.22G      -   
49.9G  -
tank/home at auto-2012-11-26_13.00.monthly                  2.47G      -   
50.2G  -
tank/home at auto-2013-01-07_13.00.monthly                  2.56G      -   
51.5G  -
tank/home at auto-2013-01-21_13.00.weekly                   1.06G      -   
52.4G  -
tank/home at auto-2013-01-28_13.00.weekly                    409M      -   
52.3G  -
tank/home at auto-2013-02-04_13.00.monthly                   625M      -   
52.5G  -
tank/home at auto-2013-02-11_13.00.weekly                    689M      -   
52.5G  -
tank/home at auto-2013-02-16_13.00.weekly                   17.7M      -   
52.5G  -
tank/home at auto-2013-02-17_13.00.daily                    17.7M      -   
52.5G  -
tank/home at auto-2013-02-18_13.00.daily                    17.9M      -   
52.5G  -

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