new option suggestion '--backup-only'

[Takeru KOMORIYA]

Hi,

On Wed, 10 Sep 2003 18:54:41 -0700
jw schultz <jw at pegasys.ws> wrote:

> > > > How about adding now option '--backup-only'  that means making
> > > > backups only and don't change any destination files?
> > > > 
> > > > (I posted similar patch a month ago, but the patch was made
> > > > for
> > > >  nightly snapshot of 20020808, which was tooo old! Laugh at
> > > >  me...)
> > > > 
> > > > I want to use rsync with LVM snapshot to make incremental
> > > > backups like below:
> > > > 
> > > >   1) Make LVM snapshot of file system and mount it.
> > > >   2) Compare it to yesterday's snapshot, and backup files
> > > >   which are
> > > >      updated or deleted.
> > > >      ex) rsync -a --delete --backup
> > > >      --backup-dir=/backup/backup_on_$DATE
> > > >   3) Delete yesterday's snapshot.
> > > > 
> > > > The problem is that LVM snapshots are read-only, so I need
> > > > rsync not to modefy any destination files.
> > > > 
> > > > I made trial patch against latest CVS, and this works fine for
> > > > me.
> > > > 
> > > > With this patch, new options '--backup-only' is added, and the
> > > > '--backup-dir' option implies '--backup' for convinience.
> > > 
> > > Let's see if i understand what you are talking about.
> > > The LVM stuff about snapshots and today vs. yesterday is
> > > snow so i'll eliminate it.  What i describe is partly based
> > > on your description of this as an extension of --backup that
> > > doesn't change the "destination".
> > > 
> > > You want to compare tree A with tree B and for those files
> > > that differ copy from tree B to an empty backup tree (tree C)
> > > with no change to trees A or B.  The result being that tree
> > > C is a sparse tree (a characteristic of --backup-dir).
> > > 
> > > If all are trees are local this would amount to
> > > 	rsync -a --compare-dest=$tree_A $tree_B $tree_C
> > 
> > Thanks for your advice! That's what I need.
> > I'm ashamed of my rash patch.
> > 
> > "--compare-dest" options looks very good, but I have one problem:
> > When I tried "rsync -a --compare-dest=$tree_A $tree_B $tree_C",
> > rsync made many empty directories in $tree_C(empty backup tree).
> > 
> > I'm going to find how to avoid creating empty directories, though
> > I may accept them...
> 
> The empty directories are there because it would be messy
> creating them only at need.
> 
> You might want to consider if another approach would be
> better than decremental backups.

I've read generator.c, and now I understood it's hard to avoid
creating empty directories.

Thanks for your advice!
-----------------------
Takeru Komoriya
 komoriya at paken.org
 http://www.paken.org/