Re: [rdiff-backup-users] Rdiff large files

[Chris Wilson]

Hi Stephen,

On Mon, 24 Sep 2007, Stephen Zemlicka wrote:

> Does rdiff transfer the whole file or just the part that changes as in
> rsync?

It just transfers the parts that have changed, but it uses a similar 
algorithm to rsync to do this (i.e. calculate the checksums of each 
block in the destination file) ...

> My situation is I need to backup over the internet.  I cannot modify the 
> server to run the rsync server on it.  Currently, my connectivity is 
> limited to a mapped drive.  Since rsync transfers the whole file, I was 
> hoping I could use rdiff to only transfer the changes and in a restore, 
> the specified change file/folder would be applied to patch the files to 
> the current version.

... and if rsync doesn't do what you want, I very much doubt that rdiff 
(or rdiff-backup) will either.

What you're trying to do won't work, because rsync, rdiff-backup and most 
similar tools will need to download the entire current remote file to 
calculate checksums for each block, to determine what needs to be 
uploaded. The backup optimises efficiency over the link between rsync 
client and rsync server, not between rsync server and the disk (which in 
your case is not local). They were not designed to do that.

Unless you can change the remote server to run something smarter than a 
simple file server daemon on it, I'm afraid you're quite stuck. You could 
do something completely different, remember what checksum each file had 
last time you uploaded it (or keep the block checksums locally) and just 
upload the changed blocks that way. But I don't think rdiff-backup will 
help you to do that, sorry.

Cheers, Chris.
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