About rsync over SSH and compression

[Tim Broberg]

Those are all good points.

A few more to consider:
1 - You may want to exert more effort compressing your rsync traffic than you would want to apply across the board in ssh.
2 - You *know* rsync supports compression on both sides. You don't necessarily control what algorithms are turned on on both ends in ssh.

I think I would lean towards doing it in the application myself.
    - Tim.

On 6/25/19, 9:11 AM, "openssh-unix-dev on behalf of JCA" <openssh-unix-dev-bounces+tim.broberg=servicenow.com at mindrot.org on behalf of 1.41421 at gmail.com> wrote:

    [External Email]
    
    
    Rsync supports the capability of compressing data before sending. So does
    OpenSSH. It would be probably be a waste of resources and time to enable
    both compression capabilities at the same time, but it is not clear to me
    whether, in general, it makes better sense to enable rsync compression or
    SSH compression.
    
    My first thought would be that SSH compression might yield better results,
    on the ground that SSH will try to cram as much data as possible in a
    channel data message, within the limitations imposed by the maximum SSH
    message size and the current window size. On the other hand, rsync might
    (and 'might' is the keyword here) resort to individual
    SSH2_MSG_CHANNEL_DATA messages for particular deltas, thus giving the
    compression code smaller amounts of data to play with every time.
    Additionally, SSH compression will be able to compress the rsync protocol
    control data, which rsync will not be able to compress (right?)
    
    Feedback on the issues above will be much appreciated.
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