[Borgbackup] Deduplication of tar files - doesn't seem to be giving good performance

[Sitaram Chamarty]

On 04/21/2016 11:15 AM, William Gogan wrote:
> I'm trying borgbackup out, and so far it's performing really well in almost all tests.
> 
> The one item where I'm seeing odd performance is for tar files. It appears not to be deduplicating except within the current archive.
> 
> Background: Our VM tool kicks out a .tar file per container. It compresses (lzo) the .tar. For discussion purposes, let's pretend it's called vm.tar.lzo

Compression changes the bytestream.  You may get lucky and the changes
only happened to files at the end of a tar file, but that's unlikely.
Depending on how many files changed, the probably that something changed
at the beginning of the tar file is pretty high.

This is what I would guess is happening.