[rdiff-backup-users] hardlink-only mode?

[Luke Scott]

Hi guys, I'm wondering how realistic this wish is, and I'm also
wondering if you could guide me on where to start coding it:

I am creating a backup appliance using a few different tools to do the
backups - Novell iFolder, SMB shares, etc. I want to use rdiff-backup to
keep historical diff's of those backups, but duplicating the data within
the backup server isn't necessary.

My hope is to create an option in rdiff-backup so that instead of the
mirror directory containing duplicates of the original data, the mirror
contains *hardlinks* to the original data. 

This option will be used in conjunction with one other feature: The
original data will be stored in directories with a "copy on write"
feature, meaning that the hardlinks in the rdiff-backup mirror directory
are effectively "read only" once they are created.

As files change on the source directories, the shared hardlinks are
removed and only then do they take up space in both the mirror *and*
source dirs.

This won't work well for large changing files, like live database files,
etc. But part of the grand scheme will be to differentiate those files
from smaller, user-readable files like documents, spreadsheets, etc. It
can be assumed that database backups already have their own diff scheme
anyway.

Ideas? Guidance?
thank you,
Luke