new option suggestion '--backup-only'

[jw schultz]

On Fri, Sep 05, 2003 at 09:40:12PM +0900, Takeru KOMORIYA wrote:
> Hi,
> 
> On Fri, 5 Sep 2003 01:10:54 -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.

-- 
________________________________________________________________
	J.W. Schultz            Pegasystems Technologies
	email address:		jw at pegasys.ws

		Remember Cernan and Schmitt