> If they don't change between runs, backuppc will pool the new instance 
> with the previous, although a full backup may still take a long time as 
> the block checksum verification is done over the whole file.  If they do 
> change and you use rsync, only the differences will be transferred (to 
> the extent that rsync can find them and resync on the matching parts in 
> a huge file), but the server will use the old copy and the differences 
> to reconstruct a full-sized copy which is slow and won't be pooled with 
> anything else.

Although this is true generally, I don't think it applies in this case.
What you say is true in the case of a single file that has changes in it.
Then rsync efficiently transfers only the delta.

But that doesn't apply in this case, because backuppc doesn't change the
existing VM image in the storage pool.  Instead, it creates an entire new
file, which then has to be transferred completely.  Even if the new file is
99.99% identical some other file in the pool, it won't help because rsync
isn't comparing that file to every other file in the pool.  It's only
comparing the source and target copies of the new file, and the target
doesn't exist yet, so it has to be copied completely from the source.

Someone please correct me if I'm wrong about that.
Andrew.


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