Incremental file updates over a network, NFS?

[Matt McCutchen]

On Fri, 2008-03-14 at 12:46 +0100, Andy Smith wrote:
>   can anyone point me at some consise info on when rsync is capable of
> performing incremental updates
> of binary files? I need to rsync over a network, and currently I have
> this over an NFS share but I suppose
> that even if binary updates are possible there not going to do much
> good as reading the remote file over
> NFS to check what needs to be updated will use the same bandwidth as
> copying the whole file.

You're exactly right.  The incremental transfer algorithm reduces the
network traffic between the rsync sender and receiver processes.  It
does not reduce (and may actually increase) traffic incurred by I/O to a
source or destination that is on a network filesystem.

> But to be honest, although I've tried to read up on it, Im still not
> really sure how rsync achieves incremental
> coping of files so Im not in a very strong position to speculate! ;)
> If someone could enlighten me that 
> would be great!!

For details on the incremental transfer algorithm, see:

http://rsync.samba.org/ftp/rsync/tech_report.ps

Matt