[rdiff-backup-users] Delete most recent increment?

[Ron Leach]

List, hello, having happily used rdiff-backup for some time, this is 
my first post.

I've made a mistake on another server (it holds our library files), 
which is backed up by riff-backup on our main server, over NFS, each 
evening.  I'd like to delete the most recent increment.  How should I 
do that?  (My reading of the manual seems to say the only delete 
command available is 'remove-older-than', which I do not want to do. 
I have done a search of the list and I found several messages about 
deletions, but to do with files, rather than deleting a specific 
increment.)

In case the context is relevant, here's what happened, but please skip 
this if not needed:

We have a Library server, and a Main server, running Debian.  Their 
filesystems are each mounted on the other, using NFS.  A file library 
of around 100GB is maintained on the Library server because frequent 
access is needed, for read purposes, in the normal course of the day; 
changes to the library are occasional, mostly additions, rarely an 
edit.  The Main server backs up the library files from the Library 
server, onto its own filesystem, each evening, picking up any library 
file additions or changes.  Rdiff-backup seems very suited to this, 
and we have been very happy with the scheme.

What went wrong:

The Library server was offline at the time of last backup attempt and 
rdiff-backup backed up an empty library (effectively thinking that all 
the library had been deleted).  The log recorded an increment change 
of around 100GB (reduction, of course, to zero).

Though this evening the Library server will be online, and 
rdiff-backup will 'sense' the presence of 100GB of files, it will 
(now, because of the last increment) treat these as 'new', and 
therefore do a complete backup again, another 100GB increment.  To be 
honest, this has happened a few times before, but at an additional 
100GB backup each time, I will run out of backup space, so I'd like to 
recover from my mistake by deleting this most-recent increment (of 
zero files).  I am expecting that, if I can delete this unwanted 
increment, rdiff-backup will continue, as normal but from its previous 
condition, thus knowing it has a live and current 100GB backup (as, 
indeed, it has, built incrementally over the years ).

Hence my question.  Is there any way I can delete the last increment, 
so that rdiff-backup performs its increment from its earlier state 
before it backed up our (then absent) library?

regards, Ron