Re: [Duplicity-talk] Feature request/discussion: Store identical files only once

[Chris Knight]

On Mon, Jun 23, 2008 at 6:43 PM, Jacob <address@hidden> wrote:
> On Mon, 23 Jun 2008 22:40:02 +0200
> "Daniel Hahler" <address@hidden> wrote:
>
>> So, I wonder if this could be added to duplicity, too?
>
> It would be very difficult. Duplicity's backups are very self-contained, and 
> are unaware of any other backups in the system. You'd have to supply some 
> sort of index file or a list of directories on the backup server to look in, 
> first of all, and then somehow link that incremental backup to another in a 
> way that it could remember for next time.
>
> In order for this to work reliably, duplicity would have to become a little 
> more complex than it is now. It would have to manage all your backups in one 
> spot, using a new central interface with its own settings and whatnot.
>
> Summary: it'd be a project. :)

How about this idea...  Duplicity essentially seems to try to mimic
rsync functionality, but with encryption and more transport protocols.
 (I only learned of duplicity a few days ago, from a page at rsync.net
which highly recommended it; so please pardon me for not being as
conversant as others if I make some mistakes or false assumptions.)
In looking at the output from 'duplicity --help' I don't see an
equivalent of the -n flag from rsync.  For those not familiar, the -n
flag does all the normal checks for a file transfer, but doesn't
actually do the transfer.  If duplicity supported that flag, it would
be almost trivial to set up a perl script that first does a -n
transfer against a primary data store, and uses the output to
determine what files it should transfer in the second pass, which
actually transfers just the subset of non-matching files into the
specified incremental store.

Or perhaps duplicity doesn't need a -n flag equivalent, perhaps using
the verify command would work.  I will futz with that tomorrow, as I'm
out of time tonight.

Basically, what I'm suggesting is rather than requesting that this
functionality be added to duplicity, this could be built around
duplicity with a little scripting.

If I put together such a tool, would anyone here care to beta test it?  :)

-Chris