Re: [Duplicity-talk] Sliding window backup strategy?

[Lars Marowsky-Bree]

On 2008-10-05T11:51:14, Timothee Besset <address@hidden> wrote:

> I am completely on board with the idea that a full backup should only be
> performed once, and that the full backup should be maintained with
> little to no extra incrementals to re-apply.
> 
> As far as implementation, a sliding window as you described is basically
> doing a full backup but spreading it over time so it hurts "less" ..

Agreed, see my other mail.

> When I suggested this same basic feature (only one full backup ever) ..
> some months ago on this list, I was thinking more along the lines of
> 'reverse delta' .. for instance like subversion does. The basic idea is
> that you always keep the latest version of the file and you maintain
> deltas going back in time towards earlier versions. That way you can
> drop the old stuff as you see fit.
> 
> I think however that such an implementation requires some server side
> intelligence, and it would be pretty hard to fit in duplicity's approach
> of a dumb untrusted remote storage (which was also one of the aspects
> that initially drew me to it)

I know how to do it with server-side intelligence. That's easy ;-)

That is essentially what my home-brewn scripts did. On the server side,
I rotated the last backup out of the way, created a tree of hard-links,
and rsync'ed into the new tree (rsync knows how to handle hardlinks).
That provides _trivial_ access to older revisions, while preserving the
lowest-possible-overhead on backup thanks to rsync.

Whenever I no longer wanted some particular snapshot, I could simply
delete it. The filesystem took care of everything else.

However, you're perfectly right - this requires server-side
intelligence, and access to the raw data on the server (trust issues),
and it's also less space-efficient than storing rdiffs for the most part
(each modified file would take the full space, _every time_); which is
exactly what I'm trying to move away from.


Thanks,
    Lars

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SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde